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So you think you can validate email addresses A journey down RFC5321

Name: So you think you can validate email addresses A journey down RFC5321
Description: Stavros Korokithakis gives a FOSDEM 2018 talk on how hard it is to validate email addresses properly, taking a tour through RFC 5321.

FOSDEM

3 videos recommended on HN

YouTube

Cited on HN 4 times, 2019–2025, never outright recommended score 0

Years with an HN recommendation, 2007–2026

Linked whenever email validation comes up as a fun illustration of how deceptively difficult it is.

Stavros Korokithakis gives a FOSDEM 2018 talk on how hard it is to validate email addresses properly, taking a tour through RFC 5321.

“illustrates the difficulty of email validation well” (HN, 2022)

4 citations · Talks · intermediate

Networking & internet infrastructure Software (other) Talks Systems, Networks & Security

4 Hacker News comments

From the HN archive; up to 20 kept per video, favoring different commenters. Recommendations first.

@StavrosK Jun 2019 Cites it

on HN thread Firefox Monitor

The email standard does include the +, yes. Here's a talk on the topic: [this video] But yes, that's why Fastmail supports the alternative syntax.

Talk on email address validity.

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@sybercecurity Mar 2021 Cites it

on HN thread I bought 300 emoji domain names from Kazakhstan and built an email service

always relevant: "So you think you can validate email addresses": [this video] Which is also why proposals to put email certs (S/MIME, OpenPGP) in the DNS led to hashing the local part, as DNS only allows ASCII and is case insensitive.

Talk on difficulties validating email addresses.

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@stavros Apr 2022 Cites it

on HN thread Stop Validating Email Addresses with Regex (2012)

I gave a very fun talk on the topic in FOSDEM (VOLUME WARNING!): [this video] It's more a joke than edifying, but it was very fun for me (and, I think, the audience), and illustrates the difficulty of email validation well.

Author's fun talk on email validation difficulty.

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@stavros Aug 2025 Cites it

on HN thread "Email is Easy" email address quiz

This is fun, but it feels suspiciously close to my old presentation about the exact same thing: [this video] Maybe it's just a coincidence, but a shoutout would have been nice if not.

Author's earlier presentation on same topic.

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