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Why regex isn't email validation

Blog post from WorkOS

Post Details
Company
Date Published
Author
Maria Paktiti
Word Count
1,548
Company Posts That Month
66
Language
English
Hacker News Points
-
Post removed?
No
Summary

Email validation involves distinct questions about syntax, domain mail capability, mailbox existence, and acceptance policy, but the most practical signup approach is to use a loose syntax check, confirm that the domain can receive mail through DNS MX and fallback record checks, and require email verification. Strict syntax rules can reject legitimate but unusual addresses while failing to detect common domain typos, whereas domain-level checks can identify nonexistent or explicitly non-mail-receiving domains with low cost and minimal false rejections. SMTP mailbox probing is unreliable because of catch-all configurations, greylisting, and provider privacy practices, and it can harm sender reputation by resembling address-harvesting activity. Disposable addresses, role-based inboxes, and aliases are policy or fraud concerns rather than deliverability issues and require separate decisions. AuthKit has adopted domain-level mail checks for signups and invitations, while retaining verification emails as the only reliable proof that an inbox exists and is controlled by the user; it also recommends reserved example domains for automated testing.

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