I noticed that their mail server took a noticeable amount of time to accept a test message after the closing .+CRLF. It's possible that they're doing a validation on your IP after all your data is submitted (probably RFC, but pushing it-?). You may be passing their validation, but the connection might be timing out. Or you may NOT be passing, probably because you have no PTR (reverse DNS) record. Many sites test for this. From Scott Perry's great DNSstuff site (http://www.dnsstuff.com/) :
>To get a PTR record, you should speak to your ISP. You could also >contact [EMAIL PROTECTED], who is in charge of the >43.30.64.in-addr.arpa. zone Sandy Please visit http://www.ipswitch.com/support/mailing-lists.html to be removed from this list. An Archive of this list is available at: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/
