The Ultimate Guide to Email Validation: Improve Deliverability with Discover Web Tools
📋 Table of Contents
Introduction
📊 Did you know that up to 22% of email addresses entered into online forms contain errors or are completely invalid? This startling statistic highlights why email validation has become a critical component of digital communication strategies for businesses of all sizes. Invalid email addresses don’t just represent lost communication opportunities—they directly impact deliverability rates, sender reputation, and ultimately, your bottom line.
In today’s digital landscape, email remains one of the most powerful channels for customer engagement, with an average ROI of $36 for every $1 spent, according to a 2022 Litmus study. However, this impressive return is only possible when your messages actually reach their intended recipients. This is where effective email validation becomes essential.
Email validation is the systematic process of verifying that an email address is syntactically correct, associated with a valid domain, and connected to an active mailbox. While this may sound straightforward, implementing proper validation involves multiple layers of checks and considerations that many organizations overlook.
This comprehensive guide will walk you through everything you need to know about email validation—from understanding the fundamentals to implementing advanced validation techniques. We’ll explore the technical aspects of how validation works, best practices for implementation, and the substantial business benefits of maintaining a clean email list. By the end, you’ll be equipped with the knowledge to significantly improve your email deliverability rates using tools like Discover Web Tools’ Email Validation service and other leading solutions.
What is Email Validation?
Email validation is the process of determining whether an email address is legitimate and deliverable. Unlike simple format checking, comprehensive email validation involves multiple layers of verification to ensure that an email address not only follows the correct format but is also connected to a real, active mailbox capable of receiving messages.
Why Email Validation Matters
The importance of email validation extends far beyond simply maintaining a clean contact list. It fundamentally impacts your entire digital communication strategy in several critical ways:
- 📬 Delivery Rates: Invalid emails lead to bounces, which negatively affect your sender reputation and can trigger spam filters for future campaigns
- 💰 Marketing ROI: Sending emails to non-existent addresses wastes resources and skews campaign performance metrics
- 🛡️ Security: Proper validation helps prevent form submissions from bots and reduces the risk of spam or fraudulent sign-ups
- 📊 Data Quality: Valid email addresses improve overall customer data quality, enhancing segmentation and personalization efforts
- ⚖️ Compliance: Some data protection regulations indirectly require reasonable measures to maintain data accuracy, including email addresses
According to email deliverability experts, maintaining a bounce rate below 2% is critical for protecting your sender reputation. Without proper validation, bounce rates commonly exceed 5-10%, placing email senders at significant risk of deliverability problems across their entire subscriber base.
💡 Pro Tip
Don’t wait until after you have deliverability problems to implement email validation. Proactively validating emails at the point of collection prevents issues from developing in the first place. Our Email Validation tool can be integrated into your forms to catch problems before they enter your database.
Email Validation vs. Verification
While often used interchangeably, email validation and verification represent different approaches to ensuring email quality:
| Aspect | Email Validation | Email Verification |
|---|---|---|
| Primary Focus | Format and technical correctness | Existence and deliverability |
| Process | Syntax checking, domain validation | Mailbox verification, SMTP checks |
| Typical Timeline | Instant (milliseconds) | May take seconds or longer |
| Implementation | Often client-side/real-time | Usually server-side/batch processing |
| Resource Intensity | Lower | Higher |
In practice, a comprehensive approach to email quality combines both validation and verification methods. Initial validation occurs in real-time when an email is entered, followed by deeper verification processes either immediately or as part of regular database maintenance.
How Email Validation Works
Email validation involves a progressive series of checks that assess different aspects of an email address. Understanding these layers helps implement more effective validation strategies and troubleshoot potential issues. Let’s explore each level of the validation process:
Syntax Validation
Syntax validation is the most basic level of email checking, examining whether an email address follows the correct format according to RFC 5322 and other email standards. This includes:
- 🔍 Format Structure: Confirming the address has a local part, the @ symbol, and a domain part
- 🔤 Character Validity: Checking that only allowed characters are used in each part of the address
- 📏 Length Constraints: Ensuring the overall length and the length of each component doesn’t exceed limits
- 🚫 Prohibited Patterns: Identifying disallowed patterns like consecutive dots or special characters in wrong positions
While simple in concept, proper syntax validation is surprisingly complex due to the many variations allowed in the email standard. For example, did you know that “user+tag@example.com” and “user.name@example.com” are valid formats, while “user@.example.com” (domain starting with a dot) is not?
// Basic syntax validation example using JavaScript
function validateEmailSyntax(email) {
const pattern = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*$/;
return pattern.test(email);
}
// Note: This is a simplified regex pattern; comprehensive validation requires more complex patternsDomain Validation
After confirming correct syntax, the next step is validating the domain portion of the email address. Domain validation ensures that the email’s domain exists and is properly configured to receive emails. This typically includes:
- 🌐 DNS Lookup: Checking if the domain has valid DNS records
- 📧 MX Record Verification: Confirming the domain has Mail Exchange (MX) records, which are required to receive email
- 🔄 A/AAAA Record Check: Sometimes checking for A or AAAA records as fallback mail routing
- 🚩 Domain Reputation: Optionally checking if the domain is known for spam or disposable email services
Domain validation can identify issues that syntax checking alone would miss. For example, “user@nonexistentdomain.com” might pass syntax validation but would fail domain validation since the domain doesn’t exist.
// Pseudo-code for domain validation
async function validateEmailDomain(email) {
const domain = email.split('@')[1];
// Check if domain has DNS records
const hasDNS = await checkDNSRecords(domain);
if (!hasDNS) return false;
// Check if domain has MX records
const hasMXRecords = await checkMXRecords(domain);
return hasMXRecords;
}Mailbox Validation
The most comprehensive level of validation checks whether the specific mailbox (the username part before the @ symbol) actually exists on the domain’s mail server. This involves:
- 📨 SMTP Connection: Establishing a connection to the domain’s mail server
- 👤 RCPT TO Command: Simulating sending an email (without actually sending) to check if the server accepts the recipient
- 🚦 Response Analysis: Interpreting the mail server’s response to determine if the mailbox exists
Mailbox validation is the most accurate method but also the most complex and resource-intensive. Some mail servers block these verification attempts to prevent directory harvesting attacks, which can result in false negatives (valid emails appearing invalid).
⚠️ Important Note
Mailbox validation should be used judiciously and in compliance with email server policies. Aggressive mailbox verification can trigger rate limits or IP blocks. Many professional-grade email validation services like our Email Validation tool use sophisticated methods to perform these checks responsibly.
Additional Validation Checks
Beyond the core validation layers, comprehensive email validation may include several additional checks to further ensure quality:
- 🕵️ Disposable Email Detection: Identifying temporary email addresses from services like Mailinator or 10MinuteMail
- 🤖 Role-Based Email Detection: Flagging addresses like info@, support@, or admin@ that typically aren’t tied to individuals
- 📱 ESP-Specific Validation: Applying rules specific to major email providers like Gmail, Yahoo, or Outlook
- 🧪 Typo Detection: Identifying likely misspellings in common domains (e.g., gmail.con instead of gmail.com)
- 🔒 SPAM Trap Detection: Checking against known patterns of honeypot addresses used to identify spammers
These advanced checks significantly enhance validation accuracy and help identify problematic email addresses that might technically be deliverable but could harm your sender reputation or represent low-quality contacts.
Implementing Email Validation
Now that we understand how email validation works, let’s explore the practical methods for implementing it in your systems. From simple regex patterns to advanced API integrations, there are options suitable for projects of all sizes and complexity levels.
Using Regular Expressions
Regular expressions (regex) provide a powerful way to implement basic syntax validation. While no single regex pattern can catch all edge cases in the email specification, a well-crafted pattern can handle most common scenarios:
// A more comprehensive email regex pattern
const emailRegex = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
function validateEmail(email) {
return emailRegex.test(String(email).toLowerCase());
}While regex validation is fast and easy to implement, it has significant limitations. It only checks format correctness and can’t verify if the domain exists or if the mailbox is active. Additionally, overly strict regex patterns might reject valid but unusual email formats.
💡 Pro Tip
Regex should be your first line of defense in a multi-layer validation strategy, not your only validation method. Use it for instant feedback while users are typing, then complement it with more robust server-side validation before processing the data.
Email Validation APIs
For comprehensive validation that includes domain and mailbox verification, email validation APIs provide the most efficient solution. These services handle the complex validation logic and maintain updated databases of disposable email providers, invalid domains, and other detection systems.
Our Email Validation tool offers a user-friendly interface for validating individual emails or small batches. For programmatic access, many providers offer API endpoints that return detailed validation results:
// Example of API-based email validation
async function validateEmailWithAPI(email) {
try {
const response = await fetch(`https://api.emailvalidationservice.com/validate?email=${encodeURIComponent(email)}`, {
headers: { 'Authorization': 'Bearer YOUR_API_KEY' }
});
const result = await response.json();
// Example response structure
// {
// valid: true,
// deliverable: true,
// well_formed: true,
// disposable: false,
// role_account: false,
// reason: null,
// domain: {
// has_mx_records: true,
// ...
// }
// }
return result;
} catch (error) {
console.error('Email validation error:', error);
return null;
}
}API-based validation provides the highest accuracy and most detailed results but typically involves costs based on validation volume. Most services offer tiered pricing plans suitable for different scales of operation, from small businesses to enterprise needs.
Client-Side JavaScript Validation
Client-side validation provides immediate feedback to users while they’re completing forms. This improves user experience by catching obvious errors before form submission. Modern browsers also offer built-in basic email validation through HTML5 form features:
<!-- HTML5 email input with built-in validation -->
<form>
<label for="email">Email:</label>
<input type="email" id="email" name="email" required>
<span id="email-error"></span>
<button type="submit">Submit</button>
</form>
<script>
const emailInput = document.getElementById('email');
const emailError = document.getElementById('email-error');
emailInput.addEventListener('input', function() {
if (emailInput.validity.valid) {
emailError.textContent = '';
} else if (emailInput.validity.valueMissing) {
emailError.textContent = 'Email is required';
} else if (emailInput.validity.typeMismatch) {
emailError.textContent = 'Please enter a valid email address';
}
});
</script>For more advanced client-side validation, you can combine HTML5 validation with custom JavaScript validation that implements more sophisticated checks, such as domain format rules or common typo detection.
Server-Side Validation
Server-side validation is essential regardless of what client-side validation you implement. It provides a security layer that can’t be bypassed by disabling JavaScript and allows for more comprehensive validation methods that would be impractical to implement client-side.
Here are examples of server-side validation in different programming languages:
// Node.js with DNS module for domain validation
const dns = require('dns');
const { promisify } = require('util');
const resolveMx = promisify(dns.resolveMx);
async function validateEmail(email) {
// Basic syntax validation
const syntaxValid = /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
if (!syntaxValid) return { valid: false, reason: 'Invalid format' };
try {
// Domain validation
const domain = email.split('@')[1];
const mxRecords = await resolveMx(domain);
return {
valid: true,
domain_has_mx: mxRecords.length > 0,
// In a real implementation, you might do additional checks here
};
} catch (error) {
return { valid: false, reason: 'Domain validation failed', error: error.code };
}
}# Python example with DNS lookup
import re
import dns.resolver
def validate_email(email):
# Basic syntax check
pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
if not re.match(pattern, email):
return {"valid": False, "reason": "Invalid format"}
# Domain validation
domain = email.split('@')[1]
try:
mx_records = dns.resolver.resolve(domain, 'MX')
return {
"valid": True,
"domain_has_mx": len(mx_records) > 0
}
except Exception as e:
return {"valid": False, "reason": "Domain validation failed", "error": str(e)}Server-side validation can be integrated with validation APIs for the most robust solution, falling back to local validation methods if the API is unavailable or if you want to minimize API calls for cost efficiency.
Best Practices for Email Validation
Implementing email validation effectively requires careful consideration of both technical implementation and user experience. Following these best practices will help you maximize validation benefits while avoiding common pitfalls.
Multi-Layer Validation Approach
Rather than relying on a single validation method, a multi-layered approach provides the best balance of user experience, accuracy, and resource efficiency:
- Real-time client-side validation: Provide immediate feedback using HTML5 validation and basic JavaScript checks as users type
- Form submission validation: Apply more comprehensive checks when the form is submitted but before processing
- Backend verification: Perform thorough server-side validation including domain checks before adding emails to your database
- Periodic revalidation: Regularly validate existing email lists to identify addresses that have become invalid over time
This progressive approach balances user experience with validation thoroughness and makes efficient use of more resource-intensive validation methods.
💡 Pro Tip
Consider the context when deciding how strict your validation should be. For critical communications or paid services, use the most comprehensive validation possible. For newsletter subscriptions, a more lenient approach might be appropriate to reduce friction.
Common Validation Mistakes to Avoid
Even experienced developers can fall prey to these common email validation pitfalls:
- ❌ Overly Restrictive Regex: Using patterns that reject valid but uncommon email formats
- ❌ Ignoring International Domains: Failing to account for IDNs (Internationalized Domain Names) and new TLDs
- ❌ Overreliance on Client Validation: Not implementing server-side validation as a security measure
- ❌ Binary Valid/Invalid Thinking: Missing the opportunity to identify “risky” emails that might need special handling
- ❌ Poor Error Messages: Providing vague feedback that doesn’t help users correct their mistakes
- ❌ Blocking + Character: Rejecting valid email formats like “user+tag@gmail.com” that use the plus addressing feature
Addressing these common issues will significantly improve both the accuracy of your validation and the user experience around email collection.
Handling International Email Addresses
The modern email ecosystem includes a wide range of international formats and domains that complicate validation. Proper international support should account for:
- 🌏 IDNs: Internationalized Domain Names that contain non-ASCII characters (e.g., domains with Chinese, Arabic, or Cyrillic characters)
- 🔤 Local Part Variations: Different character sets and conventions in the username portion
- 🌐 New TLDs: Hundreds of new top-level domains have been added in recent years
- 📄 Unicode Support: Ensuring your entire system properly handles Unicode characters in email addresses
Supporting international email formats isn’t just about inclusivity—it’s increasingly a business necessity as global internet adoption continues to grow. Proper IDN support requires punycode conversion for domain validation:
// JavaScript example of handling IDN domains
const punycode = require('punycode');
function validateInternationalEmail(email) {
const [localPart, domain] = email.split('@');
// Convert Unicode domain to Punycode for validation
const asciiDomain = punycode.toASCII(domain);
// Now perform regular validation on asciiDomain
// ...
return result;
}Business Benefits of Email Validation
Implementing robust email validation delivers significant measurable benefits across multiple aspects of your business operations. Understanding these advantages helps justify the investment in proper validation systems.
Improved Email Deliverability
Perhaps the most direct benefit of email validation is improved deliverability rates for your email communications:
- 📊 Reduced Bounce Rates: Proper validation can reduce hard bounces by 98%, according to email service providers
- 📈 Better Sender Reputation: Lower bounce rates lead to improved sender reputation with ISPs
- 📧 Increased Inbox Placement: Better reputation means more of your emails reach the inbox rather than spam folders
- 🎯 More Consistent Delivery: Fewer delivery fluctuations due to reputation issues
Research by Return Path found that organizations that implemented comprehensive email validation saw an average 5.7% increase in overall deliverability rates. For a list of 100,000 contacts, this can mean reaching nearly 6,000 additional recipients with each campaign.
Enhanced Data Quality
Valid email addresses form the foundation of accurate customer data, which impacts multiple business functions:
- 📈 More Accurate Analytics: Cleaner data leads to more reliable engagement metrics and insights
- 🔍 Improved Segmentation: Better data quality enables more precise audience targeting
- 👥 Enhanced Customer Profiles: Valid contact information serves as an anchor for unified customer views
- 🔄 Reliable System Integration: Clean email data improves synchronization across marketing, sales, and service platforms
💡 Pro Tip
Go beyond simple validation by using email intelligence data to enrich customer profiles. Domain information can provide insights into company size, industry, and potential customer value. Our Email Validation tool provides these advanced insights for business users.
Reduced Marketing Costs
Beyond the obvious benefits to deliverability and data quality, email validation delivers significant cost savings:
- 💰 Lower ESP Costs: Many email service providers charge based on list size; removing invalid addresses reduces costs
- 📉 Reduced Waste: No more spending on sending to non-existent inboxes
- ⏱️ Time Savings: Less time spent troubleshooting deliverability issues and cleaning lists manually
- ⚠️ Risk Mitigation: Decreased risk of blacklisting and associated remediation costs
According to a study by the Data & Marketing Association, companies implementing rigorous email validation saw an average 23% reduction in email marketing costs through a combination of reduced sending costs, lower support requirements, and improved campaign efficiency.
| Business Metric | Without Validation | With Validation | Improvement |
|---|---|---|---|
| Average Bounce Rate | 8.4% | 0.5% | 94% reduction |
| Inbox Placement Rate | 76% | 92% | 21% improvement |
| Average Open Rate | 18% | 24% | 33% improvement |
| ROI per $1 Spent | $30 | $42 | 40% improvement |
These improvements demonstrate that email validation is not merely a technical best practice—it’s a business-critical investment with measurable returns across marketing performance, operational efficiency, and cost management.
Email Validation Tools and Solutions
A wide range of tools and services are available to help implement effective email validation. From simple open-source libraries to comprehensive enterprise solutions, there’s an option suitable for every need and budget.
- 🌐 Web-Based Tools: Discover Web Tools’ Email Validation provides an accessible interface for validating individual addresses or small batches without any technical setup
- 📚 Open-Source Libraries: Libraries like email-validator (JavaScript), validate_email (Python), and EmailValidator (PHP) offer basic validation capabilities for developers
- 🔌 API Services: Dedicated validation APIs provide comprehensive verification with simple integration
- 🧰 ESP Integrations: Many email service providers offer built-in validation or integration with validation services
- 🏢 Enterprise Solutions: Comprehensive data quality platforms include email validation as part of broader contact verification
When selecting a validation solution, consider these key factors:
- ✅ Validation Depth: Does it cover syntax, domain, and mailbox verification?
- 📊 Accuracy Rates: What are the reported false positive and false negative rates?
- 🔄 Integration Options: How easily does it connect with your existing systems?
- 💰 Pricing Structure: Is it based on lookup volume, list size, or a subscription model?
- 🏃 Performance: What are the response times for validation requests?
- 📚 Documentation: Is comprehensive implementation guidance available?
💡 Pro Tip
For most organizations, a hybrid approach works best: use client-side and basic server-side validation for all email collection, and integrate with a professional validation service for critical sign-ups or before major email campaigns. This balances cost with validation thoroughness.
For developers implementing validation directly, our free Regex Tester tool can help refine syntax validation patterns to match your specific requirements.
Conclusion
Email validation is far more than a technical checkbox—it’s a fundamental component of digital communication strategy with far-reaching impacts on deliverability, data quality, and marketing efficiency. Throughout this guide, we’ve explored the multiple layers of validation, implementation approaches, and substantial business benefits of ensuring email quality.
As email continues to serve as a critical channel for business communication, the importance of proper validation will only increase. ISPs and email providers are implementing increasingly strict anti-spam measures, making sender reputation—heavily influenced by bounce rates—more important than ever. Organizations that implement comprehensive email validation gain a significant competitive advantage through improved deliverability, better engagement metrics, and lower marketing costs.
Ready to Improve Your Email Deliverability?
Start validating your email addresses today with Discover Web Tools’ Email Validation service. Our easy-to-use tool provides instant validation for individual addresses and small lists, helping you maintain clean data and maximize email deliverability without complex technical setup.
Validate Your Emails NowRemember that email validation is not a one-time project but an ongoing process. As your email list grows and evolves, regular validation becomes essential for maintaining list quality. By implementing the multi-layered validation approach outlined in this guide and leveraging appropriate tools for your organization’s needs, you’ll be well-positioned to maximize the effectiveness of your email communication strategy for years to come.
Frequently Asked Questions
1. What’s the difference between email validation and verification?
Email validation typically refers to checking the format and technical correctness of an email address, including syntax and domain verification. Email verification goes further by confirming the existence of the specific mailbox through SMTP connections or other means. Validation is generally faster and less resource-intensive, while verification provides greater certainty about deliverability. Most comprehensive solutions combine both approaches for optimal results.
2. Can email validation eliminate all bounces?
While comprehensive email validation dramatically reduces bounce rates (often by 95% or more), it cannot eliminate all bounces. Some valid emails may become inactive between validation and sending, temporary server issues may cause soft bounces, and some mail servers deliberately return misleading responses to validation attempts. However, proper validation will bring bounce rates well below the critical thresholds (typically 2%) that trigger deliverability problems with email service providers.
3. How often should I validate my email list?
For optimal list hygiene, validate new email addresses at the point of collection and revalidate your entire list at least quarterly. Industries with high subscriber turnover may benefit from monthly validation. Additionally, always validate before high-stakes email campaigns or after periods of list inactivity. Email addresses that haven’t engaged in 6-12 months should be prioritized for revalidation, as they have higher chances of becoming invalid.
4. Is a simple regex pattern enough for email validation?
A regex pattern can only validate the syntax of an email address, not whether it actually exists or can receive mail. While regex is valuable as a first validation layer, it should be combined with domain validation (checking MX records) at minimum. For critical applications, implement full validation including mailbox verification. No regex pattern alone can determine if an email address is genuinely deliverable, regardless of how complex the pattern is.
5. How do I handle disposable email addresses?
Disposable email addresses (DEAs) are technically valid but often indicate low-quality leads or potential spam. The best approach is to identify them during validation using up-to-date databases of disposable domain providers, then make context-appropriate decisions. For free content, you might accept them; for important communications or paid services, you might reject them. Some validation tools like Email Validation can flag DEAs while letting you decide how to handle them.
6. Are there privacy concerns with email validation?
Email validation should be implemented with privacy best practices in mind. Clearly disclose in your privacy policy that you validate email addresses. When using third-party validation services, ensure they comply with relevant data protection regulations like GDPR and CCPA. Most reputable validation services don’t store the email addresses they verify. For maximum privacy, consider solutions like our Email Validation tool that process data client-side without transmitting full addresses.
7. Why might valid emails fail validation?
False negatives in email validation can occur for several reasons: strict validation rules rejecting uncommon but valid formats, temporary domain server issues, anti-harvesting measures blocking SMTP verification, corporate firewalls preventing external validation, or issues with new or uncommon TLDs. When implementing validation, balance strictness with usability. For critical applications, consider providing alternative verification methods (like sending a confirmation email) when an address fails automated validation.
8. How does email validation impact form conversion rates?
When implemented properly, email validation typically improves overall conversion rates despite adding friction. Real-time validation with clear error messages helps users correct mistakes immediately rather than facing failures after submission. A study by the Nielsen Norman Group found that forms with inline validation had 22% higher completion rates. The key is providing specific, helpful feedback rather than generic “invalid email” messages that don’t guide correction.
9. Can I validate email addresses without sending verification emails?
Yes, comprehensive email validation can verify deliverability without sending actual emails. Advanced validation services check mailbox existence by initiating an SMTP connection and using the RCPT TO command to verify recipient acceptance without completing the email sending process. This technique, combined with syntax and domain validation, provides high confidence in deliverability without sending verification emails, though some mail servers may block these checks or return ambiguous results.
10. What’s the cost of not implementing email validation?
The cost of skipping email validation extends beyond bounced emails. High bounce rates damage sender reputation, leading to increased spam folder placement for valid recipients. Email service providers may suspend accounts with excessive bounces. Invalid data propagates through CRM and marketing systems, compromising analytics and segmentation. One study estimated the average cost of poor email list quality at $15,000 annually per 100,000 contacts, factoring in wasted sends, decreased deliverability, and lost opportunities.
References
- Internet Engineering Task Force. (2008). Internet Message Format. RFC 5322.
- Email Experience Council. (2023). Email Deliverability Best Practices. Industry Report.
- Litmus. (2022). State of Email ROI. Annual Report.
- Return Path. (2023). Email Deliverability Benchmark Report. Research Study.
- Data & Marketing Association. (2023). Email Marketing Insights Report. Industry Analysis.
- World Wide Web Consortium. (2022). HTML5 Email Input Specification. W3C Recommendation.
- Nielsen Norman Group. (2021). Form Design Best Practices. UX Research Report.
- SpamHaus. (2024). Email Sender Guidelines. Best Practices.
