On 7/28/2014 9:56 AM, Brian wrote: > On Mon 28 Jul 2014 at 14:02:29 +0200, Slavko wrote: > >> Dňa Sun, 27 Jul 2014 13:02:18 +0100 Brian <a...@cityscape.co.uk> >> napísal: >> >>> He could check with nc. >>> >>> brian@desktop:~$ nc smtp.gmail.com 25 >>> 220 mx.google.com ESMTP 19sm41008233wjz.3 - gsmtp >>> >> >> AFAIK, the port 25 have to used only for (inter-) servers connections, >> the clients have connect via 587, the port 25 for client connections is >> for backward compatibility only. > > How does the server tell the difference between talking to another > server (which is acting as client) and what you call a "client"? > >
It doesn't, but operation is quite different. MTA's typically require no login on port 25, but only allow messages to be sent to domains it serves (otherwise it quickly becomes a spam server). Port 587 requires a login, but allows messages to be relayed to any domain. Now, for historic reasons, some MTA's still allow login on port 25 (either directly or some indirect method like accessing a POP or IMAP account before sending). But these are becoming fewer and fewer. BTW, many ISP's have blocked outgoing port 25 connections (especially on residential accounts) because there are a lot of trojans out there which will install a minimal MTA on a user's machine, unbeknownst to the user. This allows spammers to use the compromised machine to be a spam source, hiding the real source of the spam. Jerry -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: https://lists.debian.org/53d65f5b.1070...@attglobal.net
