> Another wild guess would be possibly that the MTU value is too high
> and hasn't been auto-negotiated down.
[...]
> Doesn't explain how telnet connections work but exim connections
> don't. Unless the test telnet connections are only using "small"
> packets.
This is the usual case with (Unix) telnet because telnet normally sends
only one line at a time (as you type it and hit return). MTAs will
tend to send output in larger blocks; obviously the actual message,
and probably often the MAIL FROM/RCPT TO/etc sequences (with ESTMP
pipelining).
(I don't know if MTU is a plausible explanation here, this is just a
general issue.)
- cks
