[wplug] Problems sending email

[salm at servanttechnology.com]

Hi all,

I'm running qmail with courier on a Linux server co-located in downtown
Pittsburgh.  A couple weeks ago I started having problems sending email
from Thunderbird.  But, I could still send through squirrelmail.  I have
my email accounts setup with IMAP and use SSL to download email and TLS to
upload.

I have never known my email server to send/forward any spam.  I run
spamassasin on the server.  So, it shouldn't be on any blacklists.  But, I
didn't check.

So, two nights ago I thought I would just fix the problem.  So, I checked
out the server and everything looked fine.  I bounced all the email
processes.  Confirmed everything was fine but still had the same problem. 
I then bounced the server.  No help.

I tried changing Thunderbird settings by removing all security settings
just went straight STMP and IMAP.  No help either.

So, I started thinking about other common denominators.  Two other people
using my email server use Verizon and they have the same problem.  I
connect from NYC and use Verizon, again have the problem.  I connect from
home and use Armstrong Cable.  I never had a problem from Armstrong Cable,
I verified last weekend by sending an email and my wife has never had a
problem either.

Is Verizon blocking something?  Has anyone ever had a similar experience?

What blacklist site should I check?

Thanks,

Sal