So you think you can validate email addresses A journey down RFC5321
Why Hacker News recommends it
Linked whenever email validation comes up as a fun illustration of how deceptively difficult it is.
What 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.
Recommended by 0 HN commenters across 0 different months, 2019 to 2025.
What Hacker News said
Cites StavrosK · 2019-06 · on “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.
Cites sybercecurity · 2021-03 · on “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.
Cites stavros · 2022-04 · on “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.
Cites stavros · 2025-08 · on “"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.