mailexists

Mailexists is a term used in information technology to describe a capability or function that determines whether a given email address exists within a mail system, mailbox directory, or user account registry. It is not defined by a universal standard, and implementations vary across platforms, services, and programming environments.

Common approaches to mailexists include syntax validation to ensure the address conforms to general email format, DNS-based checks such as MX record lookups to confirm the domain is capable of receiving mail, and mailbox verification using SMTP to probe whether the mailbox accepts messages. Some services perform directory checks against LDAP, Active Directory, or custom user stores to map an address to a user account.

However, there are significant limitations. Many mail servers disable or rate-limit SMTP verification to prevent abuse, and some domains implement catch-all configurations that appear to accept any mailbox. Verifying existence by non-consensual probing can raise privacy and legal concerns, and results can be unreliable for purposefully obfuscated or temporary addresses. Consequently mailexists is typically used as part of a broader email-validation workflow that also considers deliverability history, bounce-detection data, and user consent.

In practice, organizations use mailexists as a hygiene measure for signup forms, marketing lists, and CRM data, but it should not be relied upon as definitive proof of an active mailbox. Related concepts include email validation, SMTP verification, MX records, and directory services.