[Exim] firewall and email problems

I don't think the version makes a difference but it's 4.14.

As I stated before (weeks ago), I'm having problems receiving emails from
some hosts through a firewall. The fireall is sonicwall.

here's a snip of the tcpdump on the connection:
13:45:22.079607 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 3497291847:3497293211(1364) ack
861468179 win 34100 (DF)
13:45:22.079813 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 1364 win 63488 (DF)
13:45:22.177076 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 1364:2728(1364) ack 1 win 34100
(DF)
13:45:22.177348 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 2728 win 63488 (DF)
13:46:22.165167 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 2728:4092(1364) ack 1 win 34100
(DF)
13:46:22.165558 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 4092 win 63488 (DF)
13:46:22.259417 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 4092:5456(1364) ack 1 win 34100
(DF)
13:46:22.259684 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 5456 win 63488 (DF)
13:47:22.292169 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 5456:6820(1364) ack 1 win 34100
(DF)
13:47:22.292497 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 6820 win 63488 (DF)
13:47:22.388905 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 6820:8184(1364) ack 1 win 34100
(DF)
13:47:22.389168 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 8184 win 63488 (DF)
13:48:22.372596 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 8184:9548(1364) ack 1 win 34100
(DF)
13:48:22.372925 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 9548 win 63488 (DF)
13:48:22.466148 relais.videotron.ca.33190 >
dial218.pm3bland1.bland.naxs.com.smtp: . 9548:10912(1364) ack 1 win 34100
(DF)
13:48:22.466446 dial218.pm3bland1.bland.naxs.com.smtp >
relais.videotron.ca.33190: . ack 10912 win 63488 (DF)

As you can see, there's a 1 minute window in which no data was transmitted.
Eventually a timeout occurs:
2003-07-03 13:22:38 SMTP connection from relais.videotron.ca [24.201.245.36]
(TCP/IP connection count = 1)
2003-07-03 13:29:12 SMTP connection from relais.videotron.ca [24.201.245.36]
(TCP/IP connection count = 2)
2003-07-03 13:34:48 19Y7tu-0000Q0-Tj SMTP data timeout (message abandoned)
on connection from relais.videotron.ca (VL-MO-MR001.ip.videotron.ca)
[24.201.245.36]
2003-07-03 13:49:22 SMTP connection from relais.videotron.ca
(VL-MS-MR002.sc1.videotron.ca) [24.201.245.36] lost while reading message
data

I'm thinking it's the sonicwall. If someone decides to help and needs to
know what model the sonicwall is and firmware, I can get that information.

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