Update: when I experienced an ISP messing with smtp traffic, they had set up a transparent proxy, which was used to rate-limit outgoing emails. However, without careful inspection of the packets, it really looked like outgoing smtp was unrestricted.
The tool to use here is tcptraceroute.
Compare the results of the following commands, when run from kamet:
Code: Select all
tcptraceroute makalu.akadia.com 25
Code: Select all
tcptraceroute makalu.akadia.com 22