According to Wikipedia Email addresses can contain comments in parentheses like john.smith(comment)@example.com.
I tried to send out some mails to valid Email addresses using such comments using several Email servers but all of them complained that the email address does not exist (Unknown address
error 550-'Requested action not taken: mailbox unavailable' (delivery
attempts: 0)>).
Do Email servers not support comments usually and what is the reason for getting this error ?
I'm somewhat guessing, but maybe this still helps you:
There are two places where the recipient address is used. First is inside the e-mail as a header-field ("To:"), second is in the SMTP dialog when issueing the RCPT command. The latter is usually called the "envelope" recipient.
RFC5322 describes the Internet Message Format (i.e. the header and content of an e-mail message), but not the SMTP protocol. In RFC5321 (which is the SMTP pendant to RFC5322) there is no mention of a comment in an e-mail address.
Thus, chances are that your servers are right, because your client should have removed the comment before using it as an envelope-address. If that had been done, your envelope-sender would be SMTP-friendly for the server to handle and the comment is still inside the e-mail (as a header) for the recipient.
