You attach a great photo, a rally shot, a candidate video, a get-out-the-vote graphic, hit send, and it lands for some voters and silently vanishes for others. No error you'll notice, just messages that didn't arrive. The culprit is almost always the same: your media was bigger than the carrier would accept.
MMS file limits are smaller and more inconsistent than most campaigns assume. Here's what you can actually send.
The limits are per carrier, and they don't agree
Every US carrier sets its own maximum MMS size, and it varies by the type of number you're sending from. Exceed the limit and the carrier rejects the message outright. Approximate maximums:
| Carrier | Long code (10DLC) | Toll-free | Short code |
|---|---|---|---|
| AT&T | 1 MB | 600 KB | 600 KB |
| T-Mobile | 1.5 MB | 600 KB | 1 MB |
| Verizon | 1 MB | 600 KB | 1.2 MB |
Notice the trap: your list is a mix of carriers and you usually can't control which. A 900 KB image sails through to a T-Mobile long-code recipient and gets rejected by AT&T. So the number that actually matters isn't any single cell in that table.
The only number to remember: 600 KB
Because your recipients span every carrier, the safe maximum is the smallest common limit: 600 KB total. Keep your media under 600 KB and it delivers to everyone, regardless of carrier or your sender type. Go over, and you're gambling on which of your voters happen to be on the right network, a gamble you'll lose quietly, with no bounce to tell you.
That's the single rule to run your program by: 600 KB or it might not arrive.
What file types actually work
Size is half the story. Format is the other half. Broadly supported across carriers:
- Images are safest: JPEG and PNG are the universal choices; GIF, BMP, TIFF, and WebP also work.
- Video works but is heavier: MP4 is the reliable format, ideally H.264. Video is where you blow the size budget fastest.
- Audio (MP3, WAV, and others) and documents (PDF, vCard, iCal) have limited and inconsistent carrier support, don't build a program around them.
One specific gotcha: animated GIFs. They often can't be auto-resized, so if an animated GIF is over the limit, it simply won't be shrunk to fit, it'll just fail. If you must send one, it has to be under 600 KB as-is.
How to stay under the limit
You have two options. The better one is to optimize before you send, so you control the quality:
- Images: resize to roughly 640×480 or smaller and export as JPEG at about 80% quality. That's plenty for a phone screen and usually lands well under 600 KB.
- Video: compress to H.264, keep it under 30 seconds, target 480p. A long, high-res clip will never fit; a short, compressed one will.
The fallback is transcoding, where the platform automatically resizes oversized media to fit the destination carrier (images become JPEG, video becomes H.264 MP4). It's a useful safety net, but it costs quality, the platform is shrinking your image blindly. Optimize first; let transcoding catch what slips through.
And the quiet truth: if there's no media, don't send MMS
A lot of "MMS problems" disappear when you ask whether you needed MMS at all. If your message is just text, send it as SMS, it's cheaper, faster, and more reliable, with fewer ways to fail. Reserve MMS for when the image or video is actually the point.
The modern answer: RCS
There's a reason this article reads like a list of workarounds, MMS is old technology with old constraints. RCS, the successor to SMS and MMS, handles rich media far more gracefully: bigger files, better quality, verified branding, and a real experience instead of a compressed thumbnail. On the carriers and devices that support it, RCS is where campaign media is headed, precisely because it erases the 600 KB tightrope this whole post is about. Until it's everywhere, though, the rule holds: for MMS, stay under 600 KB and stick to JPEG, PNG, and MP4.
Frequently asked questions
What is the maximum file size for an MMS?
It varies by carrier and sender type (from about 600 KB to 1.5 MB), but because your recipients span all carriers, the safe universal maximum is 600 KB total. Stay under that and your media delivers to everyone.
What file types can I send by MMS?
Images are safest, JPEG and PNG are universally supported (GIF, BMP, TIFF, WebP also work). MP4 (H.264) is the reliable video format. Audio and documents (PDF, vCard) have limited carrier support. Animated GIFs won't be auto-resized, so they must already be under the size limit.
Why did my picture message fail to some people but not others?
Almost always size. Different carriers enforce different MMS limits, so an image over 600 KB can deliver on one network and be silently rejected on another. Keep media under 600 KB to reach every carrier.
Carrier limits are approximate and can change; figures referenced from Telnyx's MMS documentation. Informational, not legal advice.
Keep reading: How to write your first compliant political text and SMS vs MMS vs RCS: which format to use.