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Email validation guides
Long-form notes on shipping software, running infrastructure, and learning in public.
Articles
21 postsengineering
6 min read
Unicode Email Addresses at Signup
Unicode domains become punycode via IDNA2008. A Unicode local part can still pass syntax checks. That is not an SMTPUTF8 delivery test.
Oct 2, 2026
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engineering
9 min read
How to Block Disposable Emails in Firebase
Reject throwaway emails in Firebase beforeUserCreated, before the user row exists. Abort detect at 3 seconds. Fail open if the call dies.
Sep 30, 2026
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engineering
8 min read
Which Email Providers Ignore Dots and Plus Tags
Gmail ignores dots. Proton also drops hyphens and underscores. Outlook and Fastmail strip plus tags only. Workspace domains keep dots.
Sep 28, 2026
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marketing
4 min read
What Is a Privacy Relay Email?
A privacy relay is a durable forwarding alias, not a temp-mail inbox. Apple Hide My Email is one provider. Block disposables. Decide relays separately.
Sep 25, 2026
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engineering
7 min read
How to Handle Email Validation API Errors
Map 401, 403, 429, and 5xx on detect. Two 429 codes exist. Do not retry rate limits inside the signup request. Do not tell the user their email is invalid.
Sep 21, 2026
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marketing
5 min read
What Is a Disposable Email Address?
A disposable email is a throwaway inbox, usually on a temp-mail domain. It is not plus addressing, not Apple Hide My Email, and not proof the mailbox is empty.
Sep 20, 2026
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