How do I generate long valid email address?

Question

What I mean:

$ php -r 'var_dump(filter_var(str_repeat("a", 64) . "@gmail.com", FILTER_VALIDATE_EMAIL));'
Command line code:1:
string(74) "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@gmail.com"
$ php -r 'var_dump(filter_var(str_repeat("a", 65) . "@gmail.com", FILTER_VALIDATE_EMAIL));'
Command line code:1:
bool(false)

Is there a restriction on length of a mailbox name? I need an email of more than 255 characters long (for testing).

UPD Let me explain what I need this for. I'd like to ensure in my tests that user can't specify email address longer than 255 characters. That's why I need a long email address.

UPD Following Justinas suggestion:

$ php -r 'var_dump(filter_var(str_repeat("a", 64) . "@" . str_repeat("g", 63) . ".com", FILTER_VALIDATE_EMAIL));'
Command line code:1:
string(132) "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg.com"
$ php -r 'var_dump(filter_var(str_repeat("a", 64) . "@" . str_repeat("g", 64) . ".com", FILTER_VALIDATE_EMAIL));'
Command line code:1:
bool(false)

Answer 1

To cite a little more from the link Justinas provided:

The format of email addresses is local-part@domain where the local part may be up to 64 characters long and the domain may have a maximum of 255 characters—but the maximum of 256-character length of a forward or reverse path restricts the entire email address to be no more than 254 characters long.

Now if we look at the filter_var's source, we'll see that there are basically two checks there:

1. if the entire email address is longer than 320 symbols
2. if it matches the regex (unless we specify FILTER_FLAG_EMAIL_UNICODE flag)

The regex may be rewritten as follows:

/^
  ### check if total length is no more than 254 symbols
  (?!
    (?:
      (?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)
      |
      (?:\\x22?[^\\x5C\\x22]\\x22?)
    ){255,}
  )
  ### check if the part before @ is no more than 64 symbols
  (?!
    (?:
      (?:\\x22?\\x5C[\\x00-\\x7E]\\x22?)
      |
      (?:\\x22?[^\\x5C\\x22]\\x22?)
    ){65,}
    @
  )
  (?:
    (?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)
    |
    (?:\\x22(?:[\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]|(?:\\x5C[\\x00-\\x7F]))*\\x22)
  )
  (?:
    \\.
    (?:
      (?:[\\x21\\x23-\\x27\\x2A\\x2B\\x2D\\x2F-\\x39\\x3D\\x3F\\x5E-\\x7E]+)
      |
      (?:
        \\x22
        (?:
          [\\x01-\\x08\\x0B\\x0C\\x0E-\\x1F\\x21\\x23-\\x5B\\x5D-\\x7F]
          |
          (?:\\x5C[\\x00-\\x7F])
        )*
        \\x22
      )
    )
  )*
  @
  (?:
    (?:
      ### no segment must be longer than 64 symbols
      (?!.*[^.]{64,})
      (?:
        (?:
          (?:xn--)?
          [a-z0-9]+
          (?:-+[a-z0-9]+)*
          \\.
        ){1,126}
      ){1,}
      (?:
        (?:[a-z][a-z0-9]*)
        |
        (?:(?:xn--)[a-z0-9]+)
      )
      (?:-+[a-z0-9]+)*
    )
    |
    ### ip
    (?:
      \\[
      (?:
        (?:
          IPv6:
          (?:
            (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){7})
            |
            (?:
              (?!(?:.*[a-f0-9][:\\]]){7,})
              (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?
              ::
              (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,5})?
            )
          )
        )
        |
        (?:
          (?:
            IPv6:
            (?:
              (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){5}:)
              |
              (?:
                (?!(?:.*[a-f0-9]:){5,})
                (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3})?
                ::
                (?:[a-f0-9]{1,4}(?::[a-f0-9]{1,4}){0,3}:)?
              )
            )
          )?
          (?:
            (?:25[0-5])
            |
            (?:2[0-4][0-9])
            |
            (?:1[0-9]{2})
            |
            (?:[1-9]?[0-9])
          )
          (?:
            \\.
            (?:
              (?:25[0-5])
              |
              (?:2[0-4][0-9])
              |
              (?:1[0-9]{2})
              |
              (?:[1-9]?[0-9])
            )
          ){3}
        )
      )
      \\]
    )
  )
$/iD

Knowing that the best we can get is:

$ php -r 'var_dump(filter_var(str_repeat("a", 64) . "@" . str_repeat(str_repeat("g", 63) . ".", 2) . str_repeat("g", 61), FILTER_VALIDATE_EMAIL));'
Command line code:1:
string(254) "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg.ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg.ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg"
$ php -r 'var_dump(filter_var(str_repeat("a", 64) . "@" . str_repeat(str_repeat("g", 63) . ".", 2) . str_repeat("g", 62), FILTER_VALIDATE_EMAIL));'
Command line code:1:
bool(false)