Translations:Complete Virtual Mail Server/Postfix additions/5/en

Mail submission is often incorrectly done on port 25 of the Mail Transfer Agent (MTA). Mail should actually be submitted on port 587 to the Mail Submission Agent (MSA). Postfix is both an MTA and MSA. There are numerous advantages to having mail delivered to the MSA by the client as can be seen on Wikipedia. The most important however, is that nomadic users can send e-mail even when port 25 is being blocked by a firewall, as port 587 tends to be more open. Also when only letting authenticated users send e-mail, they could even bypass the spam filter for their outgoing messages.