How do I validate the structure of an email account and what are some valid email address examples?
Matthew Whittaker
Co-founder & CTO, Suped
Published 19 Jun 2025
Updated 15 Aug 2025
7 min read
Understanding what constitutes a valid email address structure is crucial for anyone managing email lists, developing web forms, or working with email deliverability. A poorly formatted email address can lead to bounces, wasted resources, and a damaged sender reputation. It's not just about having an "@" symbol and a domain, the rules are more nuanced than many realize.
While the basic format of an email address seems straightforward (a local part, an "@" symbol, and a domain part), the specific characters and patterns allowed within each section can be surprisingly complex. This complexity often leads to challenges when trying to validate email addresses accurately, especially given evolving internet standards.
The goal of validation is to ensure that an email address adheres to established technical specifications, making it likely to exist and be capable of receiving mail. Ignoring proper validation can significantly impact your email campaigns, leading to high bounce rates and even getting your domain or IP address placed on a blocklist (or blacklist).
Anatomy of a valid email address
An email address is fundamentally divided into two main components by the "@" symbol: the local part and the domain part. Each part has its own set of rules governing allowed characters and structure.
The local part
The local part appears before the "@" symbol. It can contain a wide range of characters including uppercase and lowercase Latin letters (A-Z, a-z), digits (0-9), and certain special characters. Common special characters allowed are period (.), underscore (_), percent (%), plus (+), and hyphen (-). It's important to note that the period cannot be the first or last character, nor can it appear consecutively. For example, john.doe@example.com is valid, but john..doe@example.com is not. Also, plus addressing (e.g., myemail+newsletter@example.com) is a valid feature supported by many providers like Gmail, allowing for filtering and organization.
The domain part
The domain part follows the "@" symbol and is typically composed of a series of labels separated by periods, ending with a Top-Level Domain (TLD), like com, org, or country codes like uk. Each label can contain letters, numbers, and hyphens, but hyphens cannot appear at the beginning or end of a label. Internationalized Domain Names (IDNs), which allow non-Latin characters, have also become increasingly common.
Valid email address examples
Validating an email address goes beyond just checking the presence of an "@" symbol. While a syntactically correct email address follows the structural rules, it doesn't guarantee deliverability. A syntactically valid address might still point to a non-existent domain or mailbox.
Syntactic validity vs. deliverability
For example, test@example.com is syntactically valid according to RFCs, but if example.com doesn't exist or test is not a valid mailbox on that domain, the email will bounce. This distinction is crucial for maintaining a clean email list and ensuring good sender reputation. You can read more about RFC specifications and practical application in our blog post, What RFC 5322 says vs. what actually works.
Here are some examples of syntactically valid email addresses, including common variations and those that leverage features like plus addressing:
Standard:name@example.com
With subdomains:user@sub.domain.com
With plus addressing:john.doe+newsletter@example.org
While email addresses have strict rules, there are many common misconfigurations or types of malformed addresses that can cause issues. Identifying these is key to maintaining a healthy sender reputation and avoiding a blocklist (or blacklist).
Common errors and invalid examples
Some of the most frequent errors include missing the "@" symbol, having multiple "@" symbols, or incorrect domain structures. Invalid characters in either the local or domain part are also common. For instance, spaces within an email address are generally not permitted.
Here are examples of invalid email address structures:
Missing @ symbol:user.example.com
Multiple @ symbols:user@domain@example.com
Leading/trailing period in local part:.user@example.com or user.@example.com
Consecutive periods in local part:user..name@example.com
Invalid characters:user space@example.com
Invalid TLD:user@example.c
Methods for validating email addresses
To effectively validate email addresses, you need to employ a combination of methods. Simple client-side validation, using regular expressions (regex), is often the first line of defense to catch obvious errors in real-time.
Using regular expressions
Regular expressions are powerful for checking the structural format of an email address. A common regex pattern can check for the local part, the "@" symbol, and the domain part, ensuring they conform to basic rules. While a perfect regex for all possible valid email addresses is notoriously complex, a practical one can filter out most malformed entries. A good resource for exploring regex patterns is RegExr. If you're implementing this at the code level, check out our guide on methods to validate email accounts at the code level.
Basic email validation regexregex
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
Beyond regex: DNS and SMTP checks
For more robust validation, particularly to confirm deliverability, you can perform DNS (Domain Name System) checks to verify the domain exists and has MX (Mail Exchange) records. MX records indicate where emails for that domain should be sent. SMTP (Simple Mail Transfer Protocol) verification involves initiating a connection to the mail server to confirm if a specific mailbox is active, though this should be used with caution as it can be resource-intensive and may trigger spam filters if done incorrectly. Many email validation services and tools automate these deeper checks. For more insights on this, you can refer to this detailed article on what an email address is.
Effective email validation is a continuous effort that combines technical checks with an understanding of email standards and real-world usage. By prioritizing robust validation methods, you can significantly improve your email deliverability, protect your sender reputation, and ensure your messages reach their intended recipients.
Views from the trenches
Best practices
Always use a combination of front-end and back-end email validation for maximum accuracy and security.
Implement real-time validation on signup forms to prevent malformed or invalid addresses from entering your list.
Regularly clean your email lists by removing bounced or unengaged subscribers to improve deliverability.
Keep up-to-date with email RFCs and industry best practices, as standards can evolve over time.
Consider using email validation services for bulk list cleaning to catch hard-to-detect issues.
Common pitfalls
Relying solely on simple regex patterns, which might miss complex but valid addresses or allow invalid ones.
Not validating email addresses at the point of collection, leading to a build-up of bad data.
Ignoring soft bounces, which can eventually turn into hard bounces and negatively impact your sender reputation.
Over-validating or being too strict with validation rules, potentially rejecting legitimate users.
Failing to account for plus addressing or internationalized domain names (IDNs) in your validation logic.
Expert tips
For transactional emails, consider sending a verification email to confirm the address is active and monitored.
Monitor your bounce rates and DMARC reports to identify common validation issues affecting your sends.
Leverage domain intelligence (e.g., checking for temporary or disposable email domains) as part of your validation.
Understand that some syntactically valid emails might not be deliverable; a deeper check is often needed.
Use email validation as a key part of your overall email deliverability strategy.
Expert view
Expert from Email Geeks says that many email addresses are syntactically valid, even if they appear unlikely to be deliverable in practice.
2021-01-28 - Email Geeks
Marketer view
Marketer from Email Geeks says that Gmail addresses using the '+' alias are perfectly valid and a useful feature for users.
2021-01-28 - Email Geeks
Key takeaways
Validating email addresses is more than just a formality, it's a critical step in ensuring successful email communication and maintaining a positive sender reputation. By understanding the structural components of email addresses and implementing comprehensive validation techniques, you can significantly reduce bounces, improve deliverability, and enhance the overall effectiveness of your email marketing and transactional campaigns. Always combine syntactic checks with deeper deliverability validation to keep your email lists clean and effective.
Gmail, allowing for filtering and organization.
