Don - W9JUN
Is the Raspberry Pi the email client or the email server? server
Are you saying that if you configure the email client to use the IP address vs. DNS name, that's the difference? Or is the issue that one is the Internal IP address and the other is the external IP? If I use the local lan address for the PI the email client (which is on my phone) everything works fine with ports 25 and 110. If I use w9jun.ampr.org (22.214.171.124), the client doesn't setup.
As far as the dig command, I'm using a windows computer but here is the telnet info: My laptop is connected to my local router:
C:\Users\June>telnet w9jun.ampr.org 25
Connecting To w9jun.ampr.org... NOTHING
Got a connection to port 465
220 w9jun.ampr.org ESMTP Postfix (Debian/GNU)
Got a connection to port 110
+OK Qpopper (version 4.1.0) at w9jun.ampr.org starting.
If I switch to data on my cell I can connect to 25, 465, and 110.