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TL/DR: {64} @ {255*} =< {255}

The maximum length of an email address is 254 characters. Every email address is composed of two parts. The local part comes before the '@' sign, and the domain part follows it. In „user@example.com”, the local part is „user”, and the domain part is „example.com.” In detail:

The local part must not exceed 64 characters and the domain part cannot be longer than 255 characters; the total combined length of all characters (including '@' and punctuation) must not exceed 254 characters, however.