Some carriers require an acknowledgment when an MMS is received. If they don't get it, then they redeliver the MMS. Pulse SMS (and most other third-party apps) uses Android's built-in "system" method to download MMS so that you don't have to worry about manually entering your APN information and dealing with changes to it. For whatever reason, Google's built-in method does not provide this acknowledgment.
Pulse SMS allows you to get around this, although it does require you to input some of your APN information manually. Please follow the process below:
- Head to Settings > MMS Configuration.
- Turn on the Override System APNs toggle. This will let you input information into the fields below.
- You will need to input your carrier-specific information for the first three items: MMSC URL, MMS Proxy, and MMS Port. You can find these with a Google search for "your carrier MMS APNs".
- Turn off the toggle to Override System APNs.
The last step is very important. If you don't turn this toggle back off, MMS will probably break.