[TriLUG] location-specific SMTP problem

[Chris Merrill]

One of my co-workers has problems connecting to our SMTP server from
his house. The same Mac laptop works fine at work and most other locations.

At home he's on UVerse with an Apple router. If he turns on the hotspot
on his Verizon phone, he can connect and send mail. Turn it back off and
go through AT&T - fail.  Our office is on TWC BC -- no problems.

He can connect to other SMTP servers (GMail) without a problem. He also
reports that at certain WiFi spots, he encounters the same problem. He
does not know if those spots use AT&T or an Apple router. I've asked him
to run a traceroute next time he is on a Wifi spot that fails - to
determine if the spot is running through the AT&T network.

I connect on port 25 using STARTTLS using Thunderbird, also via AT&T Uverse
and have no problems.

This seems to narrow down the problem to a combination of our server
and either AT&T Uverse or Apple routers.

Our server is running dovecot 2.0.9 on Linux 2.6.32-431.17.1.el6.x86_64
(RHEL, I think).


I've surpassed the extent of my knowledge and it's looking like a
long deep hole of troubleshooting ahead  :(

Any ideas where I should start looking?

I'm thinking I'm going to need to capture the network traffic on his box
during an authentication session and dig into the specific messages sent/
received. But I don't really know what I'll be looking for.

TIA!
Chris

-- 
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Chris Merrill                           |  Web Performance, Inc.
chris at webperformance.com                |  http://webperformance.com
919-433-1762                            |  919-845-7601

Web Performance: Website Load Testing Software & Services
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