validation - average email address length - What is the maximum length of a valid email address?
And the segments look like this
64 + 1 + 255 = 320
You should also read this if you are validating emails
minimum length of email address
What is the maximum length of a valid email address? Is it defined by any standard?
To help the confused rookies like me, the answer to "What is the maximum length of a valid email address?" is 254 characters.
If your application uses an email, just set your field to accept 254 characters or less and you are good to go.
You can run a bunch of tests on an email to see if it is valid here. http://isemail.info/
The RFC, or Request for Comments is a type of publication from the Internet Engineering Task Force (IETF) that defines 254 characters as the limit. Located here - https://tools.ietf.org/html/rfc5321#section-4.5.3
The other answers muddy the water a bit. Simple answer: 254 total chars in our control for email 256 are for the ENTIRE email address, which includes implied "<" at the beginning, and ">" at the end. Therefore, 254 are left over for our use.