T Mobile bouncing back my emails

Yep, this has single-handedly cost me an entire month of no emails (and about 40 hours) a little over a year ago. I had to send to emails to clients, government agencies, etc. to ask if they've received my emails, because sometimes you get a bounce-back and sometimes you don't. Horrible for business. And now it's happening again.

This time it is for my work laptop 4G sim card (last time it was when I was tethering with my phone). I am going to lose clients over this and the first and second line techs, including supervisors, spend a good 5 hours each call going in circles. I KNOW WHAT THE PROBLEM IS AND THEY DON'T GET IT. It is downright scary that I know more than they do about it.

In hopes to resolve this problem (because unfortunately I need SIM card service on my laptop), I dictated what to write to the last person, which is that emails are bouncing back when sent to email addresses that are hosted by Amazon who uses Cloudmark to screen emails (and also Microsoft and others that don't send a bounce-back). I told them they need their engineering team to have the T-Mobile IP addresses delisted on Cloudmark and that it's various block of T-Mobile IPs that are on the "blacklist". I also had them write the bounceback message word for word in the trouble ticket, and to note that bouncebacks are coming from Amazon dataservers and that all IP addresses are registered to T-Mobile. Luckily, the first time this happened, I contacted my awesome hosting service who took the time to explain to me why and how it is happening and that it is something T-Mobile has to rectify (but it was a full month of frustration for me and irritated clients and agencies like the U.S. FDA).

They try to tell me I need a new SIM. They try to tell me to reboot the computer. They try to tell me to change computer settings. They did a temporary static IP address to troubleshoot, but it was so temporary that when the incompetent tech had me reboot my computer, the static IP was gone, so I could not test. They try to blame my email service. Etc.

Anyone able to get to the right people at T-Mobile to rectify? Anyone? Bueller?