dropping connection

[Lyttek]

from network A, telnet mail.domain.com 2084 (second exim running here)
server responds
type: HELO host.rmtdomain.com
server responds and further commands will send mail.

from network B, telnet mail.domain.com 2084
server responds
type: HELO host.rmtdomain.com
connection to host lost

from network B, telnet mail.domain.com 2084
server responds
type:
server responds 500 unrecognized command
type: HELO host.rmtdomain.com
server responds and further commands will send mail.


No RBL lists, ACL or anything else... problem surfaced today on a single working account. IP address of network B hasn't changed either.

No error messages in any logs that I've seen.

[Lyttek]

After three hrs of testing, here's what's up:

the ISP, rather than just blocking port 25, is resetting the connection.

Traffic to any other mail server on any port works fine until the HELO command, then the connection is reset.

Traffic to THEIR mail server works perfectly.

If you enter any command prior to HELO, which causes an error, and then process everything correctly, it works.

I have a call into the @@#$^@ ISP to find out wtf is going on...