read timeout

[Ian Lists]

This is sort of off the topic but I think this list would be the best place to ask.  On an egress mail relay I am seeing a bunch of my users mail timing out going to legit external accounts.  From the particular mail server I am able to see a full tcp session established on port 25 to the 3rd party mail servers, but they never give me the 220 message back.  If I try from personal server hosted on on a different network to the same 3rd party servers I get the 220 message right away.  I have checked every spam list I could find and only found my server's IP on apews.org bulked in with a huge Sprint /14 network.  I've seen previous posting on this list about apews.org and saw some people say that creating SPF records solved most of their issues, but it hasn't for me.  Is a server not responding back with the 220 message typical of being on a black list?  I would think if I were black listed the server would send tcp resets back or not respond back at all by just dropping the packets.  Any suggestions on how I can troubleshoot this a little further would be much appreciated.

Thanks,
Ian