Well, you'd think that would be true, but I travel frequently, and there are
actually hotels that have outsourced their guest IP service to clueless
operators that block outgoing traffic to port 25, and insist that one use
their own SMTP server (about which they fail to tell you until you get one
of their support people to answer the phone).
So I would suggest offering SMTP (AUTH) support on ports 25 and 26, just to
be sure. fastmail.fm do this -- it's a real lifesaver. But fastmail alow
and encourage their clients to send via their SMTP from any domain, which
discourages the use of SPF in any meaningful way.
SMTP-After-Pop is pointless -- it is broken in Outlook up to 2003.
From: Bernard Dugas [mailto:firstname.lastname@example.org]
Sent: Friday, February 16, 2007 8:47 AM
Subject: Re: [swinog] to SPF or not to SPF
And in complement to that, if we give to our customers some outgoing
smtp servers with authentification they can use from any hotel/wifi in
the world, there is no more reason that any email with your domain-names
are sent from other smtp servers than ours, published with SPF in DNS.
And the customer is happy because he doesn't have to change smtp server
each time he travels :-)