Email-shape rules.

What triggered this

You submitted a form with an email field whose value wasn't shaped like an email — typically a missing @, whitespace inside the address, or an empty local-part / domain-part.

The rule

Citadel performs a deliberately-light check: there must be exactly one @, with at least one character before and after, and no whitespace anywhere in the value. Every byte the form accepts is a byte SMTP would also accept.

We don't validate against a regex of every published RFC variant — those reject perfectly valid addresses, and they don't catch the most common typos anyway. The 254-byte length cap comes from RFC 5321 §4.5.3.1 and is enforced server-side.

What to try

• Confirm there's exactly one @. Two (a@b@c) or none always reject.
• Strip leading / trailing whitespace and any spaces inside the address. A copy-paste from a chat thread sometimes carries a no-break space that looks identical to a regular space.
• Make sure the local part isn't empty (@example.com) and the domain isn't empty (user@).
• If you intended to use a different field (e.g. you typed your username into an email field), correct it.

Where this fires

• Public email on your profile (Settings → Profile → Public profile).
• Billing email on an organization profile (Organization Settings → Profile → Manage).