What is the syntax of an email address (local-part@domain)?

Every email address breaks into two parts at the @ symbol. What comes before the @ is the local part (the mailbox name). What comes after is the domain (the server that receives mail for that mailbox). In captain@tidalmail.com, "captain" is the local part and "tidalmail.com" is the domain.

That's the syntax. But here's what actually matters if you're sending email: the domain side has to work in DNS. When a mail server tries to deliver a message to captain@tidalmail.com, it looks up tidalmail.com's MX records to find out where to send the message. No MX records (or broken ones) means the address can't receive mail, no matter how valid the syntax looks.

The local part is where things get interesting. Most people stick to simple names like "hello", "support", or "john.smith". But the rules (defined in RFC 5322) allow way more than that. Dots, plus signs, even some special characters are valid. The question is whether every mail server out there will accept them (spoiler: they won't always).

If you're choosing a sending address, keep it simple. "hello@yourdomain.com" or "support@yourdomain.com" will work everywhere. "hello+newsletter@yourdomain.com" usually works but can trip up older systems. Weird characters in the local part will cause you nothing but headaches.

The @ symbol itself was picked in 1971 by Ray Tomlinson when he sent the first networked email. He chose it because it was already on the keyboard and almost never appeared in people's names. (Fun fact: in 2010, the Museum of Modern Art added the @ symbol to its design collection, right next to actual art.)

If you're debugging why an address isn't working, check the domain's MX records first. That's where 90% of address problems actually live. You can use our email header analyzer to see exactly where a message failed, or just ask us if you're stuck.