[exim] SMTP command timeout on connection - how to troublesh…

One particular remote mail server seems to be having problems delivering
mail to one of my local servers running Exim. The server reports that it's
running "EdgeWave mag2700" if this matters.

I have in my Exim config:

smtp_receive_timeout = 120s
log_selector = +subject +arguments +received_recipients

Here is a log snippet, redacted:

2012-02-17 14:22:52 H=sbox.example.net [1.2.3.4] Warning: Sender rate 1.3 /
1h
2012-02-17 14:22:53 1RyUKT-0003th-B6 <= jspringsteen@??? H=
sbox.example.net [ 1.2.3.4 ] P=esmtp S=43627
id=00e901ccedb1$f272dcf0$d75896d0$@??? T="test 1A" for
jthein@???
2012-02-17 14:24:53 SMTP command timeout on connection from sbox.example.net [
1.2.3.4 ]
2012-02-17 14:24:53 H=sbox.example.net [ 1.2.3.4 ] Warning: "Connection
Ratelimit - sbox.example.net [ 1.2.3.4 ] because of notquit:
command-timeout (1.3/1h max:1.2)"

Note, that even though it says "connection ratelimit" I have this server
set to disregard ratelimits, for troubleshooting purposes, so we are
continuing to accept connections from them, with no rate limit.

You can see that the remote server connects, provides the email headers,
then seems to do nothing for 120 seconds, at which time we disconnect them.

What are my options for troubleshooting? Of course the remote mail server
admin feels that it's OUR problem. It's hard to refute that, when I have
2977 other timeout messages in my log (this 1.2.3.4 server accounts for 146
of them). Of course, probably a lot of those are spammers.

- Scott