Which is very annoying for the good guys
Having access providers funnel all SMTP traffic from their access IPs through their own SMTP gateways is the best practice. It's much worse than "annoying" with when hi-speed access providers do not block port 25 and your mail server gets hit with 10's of 1000's of connections/hour.
There is an well-known port for "mail submission", in your "services" file:
submission 587/tcp submission 587/udp
Among others, AOL listens on this port, so it's not that exotic.
You can't do this with Imail since it can only listen on one port and on all IPs (yet another plumbing feature that Ipswitch could fix/offer, rather than concentrating only on "retail checklist" features), but with IMGate you can set up mutliple SMTPD listeners, eg, on 25 and on 587, on multiple IPs, that, when coupled with IMail-pop-before-IMGate-smtp authenticated relaying, allows roaming (Imail) users on port-25-restricted IPs to relay their outbound through IMGate using whatever envelope sender.
The mail user sets his mail user agent, for a given mail account, to use SMTP server, eg, "submit.domain.com" and "port 587".
Len
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