Ahoj, Dňa Mon, 28 Jul 2014 14:56:40 +0100 Brian <ad44@cityscape.co.uk> napísal: > On Mon 28 Jul 2014 at 14:02:29 +0200, Slavko wrote: > > > Dňa Sun, 27 Jul 2014 13:02:18 +0100 Brian <ad44@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"? I don't know how server can differ the client and another server, but from abstract of RFC 6409 (which obsoletes the RFC 4409 which obsoletes the RFC 2476): Message relay is unaffected, and continues to use SMTP over port 25. When conforming to this document, message submission uses the protocol specified here, normally over port 587. And latter in the same RFC: 3. Message Submission 3.1. Submission Identification Port 587 is reserved for email message submission as specified in this document. Messages received on this port are defined to be submissions. The protocol used is ESMTP [SMTP-MTA], with additional restrictions or allowances as specified here. Although most email clients and servers can be configured to use port 587 instead of 25, there are cases where this is not possible or convenient. A site MAY choose to use port 25 for message submission by designating some hosts to be MSAs and others to be MTAs. By this i assume, that i posted formerly. As client i consider the MUA, but e.g. exim has a "client mode" too (i don't know about other MTAs). I am sorry for simplification. I want to point, that for end users is intended the 587 port, as mentioned someone other too, and IMO it is not a good opinion to suggest to try (check) the port 25, if the 587 is provided. Another goal is, that there are some ISP, which don't blocks/redirects/proxies the 587 port yet ;-) regards -- Slavko http://slavino.sk
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