Regular text messages work fine, but picture messages (MMS) get stuck with a red exclamation mark or just never arrive — this is one of the most common Android issues, and it has a very specific cause: your MMSC (Multimedia Messaging Service Center) address.
Go to Settings → Connections (Samsung) or Network & Internet (stock Android) → Mobile Networks → Access Point Names.
Find your carrier's active APN and check the MMSC field specifically — this is different from the general APN field, and it's the one most often left blank or mistyped.
Also check MMS Proxy and MMS Port — search your specific carrier to get these exact values, since they vary by carrier and are easy to get wrong by hand.
Make sure mobile data is turned on, even if you're connected to Wi-Fi — Android requires an active mobile data connection to send MMS, Wi-Fi alone isn't enough.
Check the message size — most carriers cap MMS at 1 MB. A large photo may fail silently; try sending a smaller image to confirm this is the issue.
Clear the cache for your Messages app (Settings → Apps → Messages → Storage → Clear Cache) — a corrupted cache can block MMS even with correct APN settings.
Restart your phone after making any APN changes — Android often doesn't apply new APN values until after a restart.
Yes — this specifically points to the MMSC or MMS Proxy fields being wrong, since receiving relies on push notifications while sending requires your phone to actively reach the MMSC address.
Yes. Group messaging on Android typically falls back to MMS, so the same broken MMSC settings will also break group texts even though 1-on-1 texts work fine.