If you’ve Googled this question, you probably got a bit confused.
Maybe you saw that one source says 254 characters, but other sources give different numbers (such as 255, 256, 320, etc). The reason for this confusion is the result of a mistake made in the original version of RFC 3696 where they said that the maximum length was 320.
In fact, there are technical limitations to how long email addresses can be.
The limit is actually a maximum of 64 characters in the “user part” (the one before the “@” symbol) and a maximum of 255 characters in the domain part (the one after the “@”). In other words:[user]@[mysite].com
The [user] section can be a maximum of 64 characters, and the [mysite] section can be a maximum of 255. The “@” symbol counts as the final character.
This makes a total length of 320 characters. However, there is a restriction in RFC 2821 reading: “The maximum total length of a reverse-path or forward-path is 256 characters, including the punctuation and element separators”. Since addresses that don’t fit in those fields are not normally used, the upper limit on address lengths should normally be considered to be 256, but a path is defined as:
Path = “<” [ A-d-l “:” ] Mailbox “>”
The forward-path will contain at least a pair of angle brackets in addition to the Mailbox, which limits the email address to 254 characters.
Now you know the truth behind the number 254. Hopefully, this won’t be a problem for you. Suffice to say, if your email address is 254 characters long, you’re going to want to think about shortening it, because it probably takes a long time for your users to type!