I've had a similar problem with a Paging (Inforad) Program (texting) that if I email those it will send the text, yet if I use the software (Inforad) no text arrives (Verizon) This only has begun in the past 18 mo's.
Seems it is being blocked, at the local ISP.
If I go to my Parents it works (earthlink is my smtp) as they are on earthlink
If I try it from work, No Luck
If I try it from home, No Luck (Comcast)
even tried the various ports.
I have set up Two Tone Detect and am having great success with all but sprint users. I am using the
1234567890@pm.sprint.com address(es) in the AMR email field, but no sprint users get any messages. If I send and e-mail from my outlook client to the same address with an AMR atytached, it goes through fine. Any ideas?