Valid Email
Every email term you need to master email marketing and email deliverability, explained clearly and simply.
Email Verification
Definition
A valid email address is one that is properly formatted, exists on a real mail server, and can successfully receive emails. Validity encompasses multiple factors: correct syntax following email format rules, a domain that exists and has mail server (MX) records, and a mailbox that exists and is not full or disabled. Knowing whether an email is valid before sending prevents bounces and protects sender reputation.
Types of Invalid Email Addresses
Syntax errors - Misspelled or malformed addresses (missing @, invalid characters)
Non-existent domains - Domain does not exist or has no MX records
Non-existent mailboxes - Domain is valid but the specific mailbox does not exist
Full mailboxes - Mailbox exists but cannot accept new messages
Disabled accounts - Account has been deactivated by the provider
Disposable addresses - Temporary addresses from throwaway email services
Why Valid Email Addresses Matter
Sending to invalid email addresses causes bounces that damage sender reputation. Email providers track bounce rates as a key signal of list quality and sender trustworthiness. High bounce rates lead to spam folder placement or blocking. Invalid addresses also waste marketing budget - you pay your ESP to attempt delivery to addresses that will never receive your message. From an analytics perspective, invalid addresses skew your metrics, making it harder to understand true campaign performance. Ensuring your list contains only valid addresses is foundational to email marketing success.
How Email Validity Is Determined
Email validity is determined through several verification steps. First, syntax validation checks that the address follows RFC 5321 standards - having a local part, @ symbol, and domain in the correct format. Second, domain validation confirms the domain exists in DNS and has MX records indicating it can receive mail. Third, mailbox validation connects to the receiving mail server and checks whether the specific mailbox exists without actually delivering a message. An email is considered valid only when it passes all these checks. Additional quality checks may flag valid but risky addresses like disposable emails or role-based addresses.
Best Practices
Validate email addresses at the point of collection with real-time API verification
Use client-side syntax validation for immediate feedback to users
Implement server-side mailbox verification for thorough checking
Send confirmation emails to verify the person controls the address (double opt-in)
Regularly re-verify your database as addresses become invalid over time
Remove invalid addresses immediately to prevent repeated bounce attempts
Track validity rates by acquisition source to identify problem channels
Frequently Asked Questions
What percentage of email addresses are invalid?
Studies show approximately 22.5% of email addresses become invalid each year due to job changes, abandoned accounts, and provider closures. A typical unsanitized list may contain 10-30% invalid addresses. New addresses collected without verification often have 5-15% invalid entries due to typos and fake submissions.
Can a valid email address still bounce?
Yes. An address that was valid at verification time can later bounce due to: the mailbox being deleted, the mailbox becoming full, the domain expiring, temporary server issues, or the receiving server rejecting messages based on content or reputation. This is why ongoing verification and bounce processing are important.
What is a catch-all email and how does it affect validity?
A catch-all (or accept-all) domain accepts email for any address at that domain, whether or not a specific mailbox exists. This makes it impossible to verify if a specific address is truly valid. Verification services typically mark these as 'unknown' or 'catch-all' rather than valid or invalid, indicating higher risk.
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