Is the Length of an Email Address Limited?

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Although there were several email formats used in early email systems, only one version is used now—the familiar username@example.com. The current email syntax follows standards contained in RFC 2821, and it specifies a character limit. The maximum length of an email address is 254 characters, although there has been a lot of confusion about this matter. 

Character Limitations in an Email Address

Every email address consists of two parts. The local part, which may be case sensitive, comes before the ampersand (the @ sign), and the domain part, which is not case sensitive, follows it. In "user@example.com," the local part of the email address is "user," and the domain part is "example.com."

The total length of an email address was originally stated in RFC 3696 to be 320 characters. Specifically, it said:

  • The local part of the email address—your username—must not exceed 64 characters.
  • The domain name is limited to 255 characters.
  • The ampersand counts as one character.

If you add these up, you arrive at 320—but not so fast. There is a restriction in RFC 2821, which is currently the standard in use, that says, "The maximum total length of a reverse-path or forward-path is 256 characters, including the punctuation and element separators." A forward path contains a pair of angle brackets, so that takes up two of those 256 characters, leaving the maximum number of characters you can use in an email address at 254.

So, limit the local part of the email address to 64 or fewer characters and limit the total email address to 254 characters. Anyone who has to use that email address would probably prefer you shorten it even more.

About Your Username

Although the standard specifies that the local part of the email address is case sensitive, many email clients consider the local part of an email address for Jill Smith, for example, to be the same whether the username is Jill.Smith, JillSmith or, with many providers, jillsmith.

When you choose your username, you can use uppercase and lowercase letters A to Z and a to z, digits 0 to 9, a single dot as long as it isn't the first or last character, and other special characters including !#$%&'*+-/=?^_`{|}~.