Re: Finding a replacement for my ISP's smtp server
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 <firstname.lastname@example.org>
>>> 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.