You attach a photo from your iPhone or computer, hit send, and the person on the other end gets an unopenable file icon. Here is why email clients mishandle HEIC attachments and how to make sure your photos arrive as normal JPGs.
Email apps do not agree on how to handle HEIC. Apple Mail converts HEIC to JPG automatically when you drag a photo into a message body, but sending that same photo from the Files app or a desktop webmail window attaches the raw .heic container untouched.
Windows Outlook and older webmail clients often show a blank document icon. Because HEIC uses HEVC video compression inside an image container, corporate computers without the Windows HEVC Video Extensions installed cannot render an inline preview.
Converting to JPG before you attach the file is the only guaranteed fix. Every email client made in the last thirty years can render a standard 8-bit image/jpeg inline without asking the receiver to install codecs.
How you attach the photo changes what file actually goes over the wire. iOS tries to be helpful, but its rules are inconsistent across apps.
.jpg inside the email body using Content-Disposition: inline..heic file and sets Content-Disposition: attachment.If you want your phone to stop creating HEIC files in the first place, you can stop your iPhone from saving HEIC photos in the camera settings, though that only applies to new pictures you take going forward.
When an email leaves your outbox, each file gets a MIME type header in the message source. A standard JPEG is labelled Content-Type: image/jpeg. A HEIC file is supposed to be labelled Content-Type: image/heic, though many desktop browsers and older mail servers do not recognise the extension and fall back to the generic application/octet-stream.
When classic Outlook on Windows receives an application/octet-stream or image/heic attachment, it will not render it inline in the reading pane. Even if the receiver double-clicks the attachment to open it, Windows has to hand the file off to the Photos app. On locked-down office PCs where the Microsoft Store is blocked, the machine often lacks the paid HEVC Video Extensions required to decode the 10-bit image stream inside the file. If the receiver is stuck at that exact screen, our guide on dealing with HEIC on Windows explains what is missing on their system.
| How you attach the photo | MIME type sent | What a Windows Outlook receiver sees |
|---|---|---|
| iPhone Photos app Share sheet to Apple Mail | image/jpeg | Photo displays directly inside the email body |
| iPhone Files app or desktop browser upload | image/heic or application/octet-stream | Attachment icon at the top; fails to open without codecs |
| Converted to JPG before attaching | image/jpeg | Opens cleanly in the reading pane and previewer |
Most major email providers—including Gmail, Outlook.com, and Yahoo—enforce a strict 25 MB limit per message, while many corporate Exchange servers cap incoming mail at 10 MB or 20 MB. What trips people up is that a 25 MB limit does not mean you can attach 25 MB of photos.
Email protocols were designed for 7-bit text, so every photo attachment must be converted into text using Base64 encoding before it is sent. Base64 represents every 3 bytes of binary photo data as 4 ASCII characters. That adds roughly one-third to the size of every attachment in transit. When you convert your HEIC files to JPG before emailing them, keep an eye on the final file sizes if you plan to attach a whole album to a single message.
.heic files you want to email. If you are attaching several photos to one email and need to keep the total file size down for your mail server, adjust the quality slider before dropping your files..jpg files and attach those to your email instead of the originals.Because the conversion runs entirely inside your browser tab, private photos you are emailing to an accountant, doctor, or client are never uploaded to a third-party server along the way.
Save the person on the other end from hunting for codec installers or replying that your attachments are broken. Head to heicjpg.dev, drop your HEIC files into the box, and attach the standard JPGs you get back.
Your photos are decoded in your own browser — open the converter and see.
First published: 21 October 2026