email max length

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Maximum e-mail length is 320 characters (octets).


    64 + @ + 255 = 320
    ^         ^
    |         |
 username  hostname


Quote:

    4.5.3.1.1.  Local-part

       The maximum total length of a user name or other local-part is 64
       octets.

	4.5.3.1.2.  Domain

       The maximum total length of a domain name or number is 255 octets.


Source:

	https://www.rfc-editor.org/rfc/rfc5321#section-4.5.3