450 - greylisted

this is in the source code:

// Any 4xx error also means we couldn't really check^
// except 450, which is explcitely a non-existing mailbox:^
// 450 = "Requested mail action not taken: mailbox unavailable"^
ereg("^4", $to) && !ereg("^450", $to)) {^

but this isn't right, it should be like this:
450 Requested mail action not taken: mailbox unavailable (e.g., mailbox busy)
550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)

I did a quick google on the SMTP codes, here is a handy reference:

http://email.about.com/cs/standards/a/smtp_error_code_2.htm

(from the first page of that link) the first number: 4: The server has encountered a temporary failure. If the command is repeated without any change, it might be completed. Mail servers can use such temporary failures to keep untrusted senders at bay.
5: The server has encountered an error.

So actually both 450 and 550 are valid codes, the difference is that 450 is "temporary". I would say it is probably safe overall to allow 450 codes, especially since the known greylisting issue. although I still like the idea of checking for the "greylist" keyword along with 450 to be sure that was the issue.

Ahh. had to read again what was posted, that appears correct. basically if the server is inviting you to try again later, well email verify should take that as a good response. ok now I am in favor of just removing that whole 450 part.