For S&G, look at your APNs.
My guess is you have one labeled something like "T-Mobile US 260" and that one has your protocol set to IPv4/IPv6 (or maybe IPv4?).
Look at the T-Mobile MMS one and set that one to IPv4/IPv6 [or IPv4 only].
Most foreign countries aren't on IPv6 yet and I'm guessing it's trying to send via IPv6.
No, didn't work.
I don't know about this, but in the APNs, where it says T-Mobile MMS (FYI/Extra info, it says TMUS under it), There's no option for selecting it, such as a circle, and when I press it, it gets filled. Is that normal, or is something wrong with this APN?
Didn't say to select it -- just said to edit it.
My phone has the lack of selectable option for T-Mobile MMS as well.
I did notice that MMS isn't filled out in the two selectable options, so I'm guessing it's separated out for some reason with the Nexus devices. But, I can go in to the T-Mobile MMS one (which has MMSC filled out) and change to IPv4. That's the suggestion I made.
After that, I'd be grasping at straws.
If you are roaming internationally, are picture messages (MMS) subject to the same 128 kbps throttle as data? If they are, I can see them timing out with some of the megapixel cameras that phones have these days.
Can you check the size of the photos you're sending? They may be too large send. Also, have you tried sending to other numbers? Let us know if you need more help. Thanks.