What characters are allowed in an email address?

The local part may include letters, numbers, and certain symbols such as periods and plus signs. More complex characters can appear when the address is quoted. The domain side must follow DNS rules which allow letters, numbers, and periods.

According to RFC 5322, the local part can technically contain many special characters, including \!\#$%&'\*+/=?^\_{|}\~\`. Even quoted strings with spaces are valid such as "this is valid"@tidalmail.com although no real system today would ever allow it.

Modern systems accept a broad set of characters although wise senders keep local parts simple to avoid filtering issues. Think of it as keeping the ship name easy to read when painted on the hull.