In addition to supporting end-to-end encrypted messages and calls with other Signal users, Signal Android can be configured as your default SMS/MMS app. In this case, you can send and receive insecure SMS/MMS in Signal Android. Learn how to distinguish when communication is private (Signal message) or insecure (SMS/MMS).
Sending or Receiving MMS
- Is your mobile data turned off? Do you see "unable to connect to MMS server"?
Check your phone's settings and make sure Cellular data or Mobile data is on. MMS requires a connection to your mobile network unless you are using a provider-specific app that allows you to connect over WiFi. - Are you using the latest OS update for your phone?
Check your phone settings to confirm you have the latest Android OS for your phone. - Do you have a firewall?
For example: No-Root Firewall. If you do, then you may need to disable it to download MMS. MMS requires a connection to your mobile network. - Are you over the MMS size limit?
Signal has an MMS file size limit of 300kb.
Download failed
- See the bullet points in Sending or Receiving MMS above
- Have you restarted your phone?
For some devices, if you restart your phone then re-download the MMS, it will succeed. - Do you have another app that can read MMS? i.e. Textra
Even if the other app is not open, it may still attempt to retrieve the MMS before Signal can. Check your other app. - Are media download settings set to use mobile data?
Go to Signal > Menu
or 
> Settings > Chats and media > Tap on "When using mobile data" and enable your choice of images, audio, video, documents. - Configure APN Settings
Android phone Settings > Under Wireless & networks choose "more" or on some devices go to the option where it says Mobile Networks > Choose Access Point Names > Select New APN and Enter the APN Settings required for your carrier - Ask your provider to reprovision your device
Call your mobile provider to have them refresh your APN settings and/or reprovision your device. - Delete all APNs & have your mobile provider reset it
Delete all listed APNs, restart your phone, then have your mobile provider reset your APN settings.
App crashes
- Place phone in airplane mode and delete the offending message
Place your phone in Airplane mode, then Open Signal. Find the message you just received, long-press to highlight the MMS message and tap the trash can to delete. Then take your phone out of airplane mode. - Receive a new message and mark all as read
After receiving a new message, use the notification or quick reply functionality to mark all messages as read
Provider-specific
- Are you using Tmobile?
Is MMS only working on mobile data? Then enable "WiFi calling" on your phone AND through Signal's Settings > SMS and MMS > enable WiFi calling compatibility mode
Phone-specific guides
- HTC One: https://devicehelp.optus.com.au/web/htc-one-m8/messaging/mms/setting-up-my-mobile-phone-for-mms/
If you still have an issue please submit a debug log.