Re: Finding a replacement for my ISP's smtp server
On Mon 28 Jul 2014 at 10:34:03 -0400, Jerry Stuckle wrote:
> On 7/28/2014 9:56 AM, Brian wrote:
> >
> > 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.
Would I be correct in thinking MTAs only talk to each other over port
25?
Would I also be right that using port 587 mandates authentication
whereas with port 25 it is optional?
> 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.
Port 25 then becomes used only for incoming messages to be sent to
domains the server is responsible for? If so, that doesn't appear any
different from the present situation. For relaying a login is perfectly
understanable, but it can be done on port 25 too. What makes port 587
necessary?
All my mail from home is sent directly using exim which, as far as I can
make out will only send on port 25. Leaving aside what you say below (my
ISP does not block outgoing port 25 traffic) I should not be affected?
> 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.
So, in world where every ISP blocks outgoing port 25 connections the
delivering of one's own mail becomes impossible. The flow of spam and
malware across the net will continue to increase though, I suppose.
Reply to: