SMTP not relaying SMS text messages
Heya guys, thanks in advance for any assistance on this. I'm getting a weird behavior that just started happening last month. I have a MS Server 2019 (on premise VM) that is setup as a SMTP relay. The relay sends it up to o365. The SMTP software used is hmailServer. To test, i use a simple command line utility called blat.exe. When testing, it works great to a regular email address, and it comes across fine. But when i attempt to use an email address in SMS text format, it doesn't work. The logs in the SMTP server shows that it is being sent off without errors.
In Outlook, i am able to send an email directly to those SMS email addresses.
In hmailServer interface, i do not see anything that would be blocking to those types of addresses, and went so far as to whitelist them during the troubleshooting process; of course to no avail.
The fact that it works with one type of email address, and not another type throws the whole thing off.
I was going to ask if there's a setting in o365 that prevents SMS email addresses from being used, but as mentioned, it is working when sending a direct email from Outlook bypassing the SMTP server. Perhaps I'm not thinking granular enough? Is there something in o365 that prevents SMS text via SMTP?
Thanks for all the help