The short answer
MMS requires mobile data to be switched on, even when you are on Wi-Fi, because it travels over the carrier’s network rather than the internet. Turn mobile data on, check the APN settings match your carrier’s published values, and make sure the message is not too large for the carrier’s limit.
Picture messaging is an old technology carried over a separate channel from ordinary internet traffic. That is why it fails in ways that seem to make no sense: the phone has a perfect Wi-Fi connection, everything else works, and the photo will not send.
Fix 1: mobile data
MMS is delivered over the carrier’s data network using a dedicated access point. If mobile data is switched off, or if you are out of allowance in a way that blocks data, MMS fails regardless of Wi-Fi.
Turn mobile data on
Even at home on Wi-Fi. This is the single most common cause.
Check you are not in data roaming with roaming disabled
Abroad, MMS needs roaming data enabled, which is worth knowing before a holiday rather than after.
Check the data allowance
Some carriers block data entirely when the allowance is exhausted, which takes MMS with it.
Check data saver is not restricting the messaging app
It can block background data for specific apps, and messaging is a common casualty.
Fix 2: APN settings
The access point settings tell the phone how to reach the carrier’s MMS gateway. They are configured automatically in most cases and go wrong after moving a SIM to a different phone, using a phone bought abroad, or a factory reset.
Your carrier publishes the correct values, which include an MMSC address, an MMS proxy and a port. Entering them manually takes a couple of minutes. While you are there, delete any duplicate or leftover APN entries, since the phone may be using the wrong one.
After changing APN settings, restart the phone. The messaging stack reads them at startup on many devices, and changes that appear not to work often simply have not been picked up yet.
Fix 3: message size
Carriers impose a size limit, commonly between 300KB and 1MB, and a modern phone photo is several megabytes. Phones compress images for MMS automatically, and a video or a burst of photos can still exceed it.
Signs: text messages send fine, small images send, and videos or multiple photos fail. Sending one item at a time, or a shorter video, confirms it.
Where you need to send something larger, a link to a shared album or a file sharing service is the practical answer, and it is what modern messaging apps do behind the scenes anyway.
Fix 4: group messages
A group message with pictures becomes an MMS conversation, and group MMS has its own setting that can be off. On Android it is in the messaging app’s settings, usually called group messaging or MMS. With it off, the phone sends individual messages instead, which confuses everyone in the group.
Fix 5: RCS and modern messaging
RCS is the modern replacement that sends images over the internet properly, with no size limit and no MMS involvement. When RCS is working between two people, MMS is not used at all.
Problems arise at the boundary: an RCS message to someone without it falls back to MMS, and if MMS is broken, that fallback fails. Checking whether RCS is enabled and connected in your messaging app’s settings is worthwhile, because a stuck RCS registration produces strange behaviour.
On iPhone, messages to other iPhones use iMessage, and messages to Android phones use RCS where supported or MMS otherwise. A green bubble that will not send a photo is an MMS problem even though everything else works.
Fix 6: the phone and the app
- Clear the messaging app’s cache, which resolves a stuck send queue.
- Delete very long conversation threads, since an enormous thread can cause failures on some devices.
- Check storage, because MMS needs space to assemble the message and a nearly full phone fails silently.
- Check the default messaging app, since having two installed can leave MMS handled by the one you are not using.
- Reset network settings as a last resort, which restores default APN values along with clearing saved networks.
Before resetting network settings, note that it clears saved Wi-Fi passwords and Bluetooth pairings as well as mobile settings. Try the APN values manually first, since that is the specific change rather than a broad one.
Why do I need mobile data on to send a picture on Wi-Fi?
Because MMS travels over the carrier’s data network through a dedicated gateway rather than over the internet. Wi-Fi cannot carry it, so mobile data must be enabled.
Why do small pictures send but videos fail?
Carriers limit message size, commonly under 1MB. Phones compress images to fit and videos frequently exceed the limit even after compression.
What are APN settings and where do I get them?
They tell the phone how to reach the carrier’s data and MMS gateways. Your carrier publishes the correct values, and entering them manually takes a couple of minutes.
Why did MMS stop working after I changed phones?
The APN settings did not transfer, or the new phone selected the wrong profile. Entering the carrier’s published values manually resolves it.
Does RCS replace MMS?
For messages between people who both have it, yes, and it sends images at full quality over the internet. Messages to anyone without it still fall back to MMS, which is why MMS still needs to work.
The order
Turn mobile data on, which fixes most cases immediately. Check and if necessary enter the carrier’s APN settings manually, then restart the phone. Try sending one small image to test the path, then work up to find the size limit. Check group messaging is enabled if the failure is in a group. And reset network settings only after the specific fixes, since it clears far more than the MMS configuration.
