Outlook shows “The file you’re attaching is bigger than the server allows. Try putting the file in a shared location and sending a link instead” when the attachments add up to more than its limit: 20 MB by default for internet accounts such as Outlook.com and Gmail, and 10 MB by default for Exchange work accounts. For photos, the fastest fix is to send smaller copies: resize them to a sensible pixel size and save them as JPEG at a reasonable quality. OpticBatch from Automata Labs does that for a whole folder at once on your PC, shows the estimated size savings before you run it, and never overwrites the originals.
Turn a folder of full-size photos into email-ready copies in one pass.
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What does the error mean?
Microsoft’s troubleshooting article Attachment size exceeds the allowable limit error explains the message and its two causes:
- Internet email accounts (POP3, IMAP, HTTP): “Outlook 2013 and later versions have a default attachment size limit of 20 megabytes (20480 KB).” The limit “applies whether you are adding one large attachment that is greater than 20 megabytes (MB) or several attachments whose sum total size is greater than 20 MB.”
- Microsoft Exchange accounts: the error appears by default “if the sum total of the attachments is greater than 10 MB,” based on the maximum send size your Exchange administrator configured.
Microsoft’s Reduce attachment size page adds: “This limit includes both the size of the attachment and the size of the email.”
So ten phone photos at a few megabytes each can trip the limit even though no single photo is large.
What are the limits in other email services?
| Service or account | Default limit | Source |
|---|---|---|
| Outlook with internet accounts, such as Outlook.com | 20 MB | Microsoft |
| Outlook with an Exchange work account | 10 MB by default, set by the administrator | Microsoft |
| Personal Gmail | 25 MB | |
| Google Workspace | Set by the administrator |
Google’s help page on sending attachments in Gmail says the limit for personal accounts is 25 MB, and “if your total attachment size is greater than the limit, Gmail automatically removes the attachment and adds it as a Google Drive link in the email.”
Keep in mind that the recipient’s server has a limit too. A message your server accepts can still bounce if theirs is smaller.
Why are attachments bigger than the files themselves?
Email was designed for text, so attachments are encoded as text before they are sent. The standard method, base64, is defined in RFC 2045: “The encoding process represents 24-bit groups of input bits as output strings of 4 encoded characters.” Three bytes become four characters, so an attachment takes about a third more space in the message than on your disk.
The practical lesson is to leave headroom. Do not aim for 19.9 MB of photos against a 20 MB limit.
Can I just raise Outlook’s limit?
For internet accounts, Microsoft documents a registry value, MaximumAttachmentSize, that changes Outlook’s own limit. But Microsoft also explains why the default exists: it “prevents your computer from continually trying to upload very large attachments that exceed the limits of most Internet service providers.” Raising Outlook’s limit does not raise your mail provider’s or your recipient’s. For Exchange accounts, only the administrator can change the limit.
For photos, making the files smaller is the more reliable fix.
What are the built-in ways to make photos smaller?
Microsoft lists several options, and they work differently.
- Classic Outlook: attach the images, then go to File, Info, and under Image Attachments select Resize large images when I send this message. This reduces the file size of attached images when you send.
- New Outlook: Microsoft says you can change the display size of an inserted picture, “but you cannot reduce the file size of that image.” Dragging the corners makes it look smaller, not weigh less.
- Compress to ZIP: Microsoft suggests zipping files. For photos this usually saves little, because JPEG files are already compressed.
- Share a link: upload to OneDrive or another cloud service and send the link.
The classic Outlook option is handy for a one-off message. It does not help if you use new Outlook, webmail, or another app, and it does not give you copies you can reuse.
How small should photos be for email?
It depends on what the recipient will do with them.
| Purpose | Long edge in pixels | Format | Notes |
|---|---|---|---|
| Viewing on screen | 1600 to 2048 | JPEG | Looks sharp on most screens |
| Quick previews or many photos | 1024 to 1280 | JPEG | Fits many images in one message |
| Printing at home | Keep original size | JPEG | Use a link instead of an attachment |
| Graphics with text or flat color | Original or 2048 | PNG | PNG is better for screenshots and logos |
The pixel arithmetic shows why resizing works. A 12-megapixel phone photo is about 4032 by 3024 pixels. Resized to 2048 pixels on the long edge, it becomes 2048 by 1536, which is about a quarter as many pixels. File size does not scale exactly with pixels, but a reduction of that size usually shrinks the file a lot.
For the choice between formats, see WebP vs JPEG vs PNG. For email, JPEG is the safe choice, because every recipient can open it.
How do I batch resize photos for email with OpticBatch?
OpticBatch is a local bulk image resizer and converter for Windows 10 and Windows 11. Its Microsoft Store listing describes:
- Resizing by Max Width, Max Height, Percentage Scale or Exact Dimensions, with an aspect-ratio lock to prevent distortion.
- Batch conversion between JPEG, PNG and WebP.
- A global quality slider (1 to 100) for lossy formats, “complete with a live estimation of your file size savings” before you start.
- Fault-tolerant execution: a corrupted file is flagged and the rest of the batch continues.
- A strict atomic write protocol: “Original files are never overwritten or corrupted if a batch is cancelled or interrupted.”
- Local processing: no cloud uploads, no forced account and no telemetry.
A simple email preset:
- Drop the folder of photos into OpticBatch.
- Choose Max Width and Max Height of 2048 pixels, with the aspect ratio locked.
- Set the output format to JPEG and the quality to around 80.
- Check the estimated savings, then run the batch.
- Attach the new copies, and add up their sizes before you send.
If the total is still over the limit, lower the pixel size or split the photos across two messages.
Resize, convert and compress whole folders locally, with your originals left untouched.
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Should I remove photo metadata before emailing?
It is worth thinking about. Photos from phones often carry the GPS location where they were taken. Resizing does not necessarily remove it, depending on the tool and settings. If you send photos to people outside your family or company, check for location data first. Our page on stripping EXIF from email image attachments covers that workflow.
Frequently asked questions
What is the attachment limit in Outlook?
By default, 20 MB for internet email accounts and 10 MB for Exchange accounts, according to Microsoft. The limit counts the total of all attachments plus the message.
Why does zipping my photos not help?
JPEG photos are already compressed, so a ZIP file of them is usually only a little smaller. Resizing reduces the actual image data.
Does dragging a picture smaller in Outlook reduce its size?
In new Outlook, no. Microsoft says it changes the display size but not the file size. Classic Outlook has a separate option to resize large images when sending.
What if I need to send full-resolution photos?
Use a shared link instead of an attachment. Gmail does this automatically for attachments over 25 MB.
Does OpticBatch upload my photos?
No. It processes images locally on your PC, with no cloud uploads.
Try OpticBatch
Get OpticBatch from the Microsoft Store. It is a one-time purchase with no subscription, and the Store listing shows the current price.
For more batch resizing approaches, read an ImageMagick alternative for batch resizing on Windows.
Email-ready photos in seconds, without sending your files to an online converter.
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Microsoft and Outlook are trademarks of the Microsoft group of companies. Gmail and Google Drive are trademarks of Google LLC. OpticBatch is not affiliated with or endorsed by Microsoft or Google.
Last updated 22 October 2026. Published by Automata Labs, a software company in Canada.