Why Email Validation Is Hard by @jshauma

From an article titled “Your E-Mail Validation Logic is Wrong“ dispelling our notions about the ease of email validation.

1. Email addresses can contain multiple ‘@’ symbols
2. Bang paths – addresses with ‘!’ – may be accepted
3. The percent sign may lead to relaying
4. Various punctuation characters are allowed. '*+-/=?^_`{|}~#[email protected] anyone?
5. Plus signs aren’t special, except when they are
6. Dots are special
7. Quoted strings let you break the rules
8. and more…

The original goes into interesting detail and there’s a lively discussion on r/programming:

Your E-Mail Validation Logic is Wrong from programming

More on the topic:

• What is email validation and why is it important?
• 6 mistakes you’re probably making with email validation