MMS problem verified with AT&T.
Device: Nexus 5
Carrier: AT&T
Version: Android L
Build # : LPV79
APN Settings
....have been verified as "TRUE" with AT&T. I have also tried other values without success.
FAILED
APN Protocol
....I have also tried to switch the protocol value from "IPv4" to "IPv4/IPv6"
FAILED
Texting App
.....I have also tried switching between "hangouts", "textra", and "whatsapp". Textra, when I toggle MMS delivery reports on displays the following, "MMS Message not recieved. Please check APN settings.
FAILED
I was getting quite exhausted when nothing seemed to help. :-!
Alas, after seeing your post here my mind has been put to rest. Thanks!