We recently switched ISPs and in doing so got assigned a different static IP address. That's when the problems began. Some emails go through without a hitch. Gmail for example delivers normally. There are others, however, that get hung up in the queue displaying errors like:
"The connection was dropped by the remote host."
"The remote server did not respond to a connection attempt."
"Unable to bind to the destination server in DNS."
Also, if I send the email on my phone using the same email address (but a different SMTP server, AT&T's) then it goes through fine as well.
I used telnet to check port 25 and the connection and it works just fine. And like I mentioned, some mail goes through fine, but certain domains refuse to work properly. I have contacted Frontier (our ISP) and they said our Reverse Lookup was set up, but I'm not convinced as this looks like that sort of issue. Any suggestions?