Manatee

Email attachment size limits by provider (2026)

· 6 min read

Most email providers cap a message at 20 to 25 MB, and the real ceiling for the attachment itself is lower because encoding adds about a third to its size. Gmail and Yahoo allow 25 MB per message, Outlook.com and iCloud Mail allow 20 MB, and work accounts on Microsoft 365 depend on what your administrator set. Anything bigger needs to be shrunk or sent as a link.

The limits, provider by provider

These are the published limits at the time of writing. Providers change them occasionally, so if a message bounces, check the bounce text; it usually states the limit that was exceeded.

  • Gmail: 25 MB per message, all attachments combined. Attach something larger and Gmail offers to upload it to Google Drive and insert a link instead. Gmail will receive messages up to 50 MB from other providers.
  • Outlook.com (personal Microsoft accounts): 20 MB per message. Larger files are offered as OneDrive links.
  • Microsoft 365 and Exchange (work and school accounts): set by your organization’s administrator. Defaults fall in the 25 to 35 MB range and can be raised to 150 MB, but many organizations set them lower than the default. Your IT desk can tell you the number.
  • iCloud Mail: 20 MB per message. Mail Drop, built into Apple Mail, lets you send files up to 5 GB as a temporary download link that expires after 30 days.
  • Yahoo Mail and AOL Mail: 25 MB per message.
  • Proton Mail: 25 MB total per message, with a cap on the number of attachments.

The receiving side matters too. If you are on a provider with a generous limit and the recipient’s server accepts less, the message bounces from their end, often after a delay.

Why a 20 MB file bounces from a 25 MB limit

Email was designed for text. Attachments are converted to text using base64 encoding before sending, and base64 makes data about 33 percent larger. A 20 MB video becomes roughly 27 MB of message, which is over Gmail’s 25 MB limit even though the file on your desk is under it.

Providers apply their limit to the encoded message, not to the file in Finder. The practical rules of thumb:

  • On a 25 MB limit, keep the total of all attachments under about 18 MB.
  • On a 20 MB limit, keep it under about 15 MB.
  • Leave some extra room for the message text, signatures and inline images.

This is also why “it was under the limit” is the most common confused complaint about attachment bounces.

Option one: send a link instead

For anything over the limit, every major provider now pushes you toward a link. Gmail inserts a Google Drive link, Outlook uses OneDrive, and Apple Mail offers Mail Drop automatically when an attachment is too large for the account.

Links work well when the recipient is comfortable clicking them and the file does not need to sit in their mailbox permanently. They work poorly when the recipient is a portal or a form that expects an attachment, when a company firewall blocks cloud links, when the link will expire before the recipient gets to it, or when you would rather not upload the file to a cloud account at all.

Option two: make the file smaller

If the file has to travel as an attachment, it has to fit. What “fit” takes depends on the type.

Video is the usual offender. A one-minute iPhone clip at 4K is around 300 to 400 MB, and even 1080p runs tens of MB per minute. Getting under 18 MB means a lower resolution, a lower bitrate, or both. Manatee has a Shrink mode built for exactly this target: drop the video on it, type the size you need (say 18 MB), and it finds the quality that fits and writes a new MP4 alongside the original. It will not cut the length of the clip; if a fifteen-minute video needs to fit in 18 MB, the result will look rough, and the honest answer is to send a link or trim it in an editor first. How to compress a video to email it from a Mac goes through the trade-offs.

PDFs bloat because of embedded photos and scans. Manatee’s Shrink mode also takes PDFs to a named size; Preview’s File > Export > Quartz Filter > Reduce File Size is the built-in alternative, though it offers no control over how much quality goes. See How to compress a PDF on a Mac.

Photos from an iPhone are 2 to 4 MB each, so ten of them overflow a 25 MB limit. Apple Mail offers an Image Size menu (reduced sizes up to Actual Size) when you attach photos; the Medium setting is usually plenty for viewing. Converting HEIC to JPEG does not by itself save space, since HEIC is already the smaller format.

Office documents are usually large because of the images inside them. Word and PowerPoint both have a Compress Pictures command that reduces embedded images in place, which is often enough on its own.

Zip archives rarely help with video, photos or PDFs, because those are already compressed. Zipping a folder of Word documents or text files, on the other hand, can cut the size dramatically.

Checking a file’s real size before you attach it

  1. Select the file in Finder and press Command-I.
  2. Read the Size line. Finder reports in MB using decimal units, which is what mail providers use too.
  3. Multiply by 1.33 to estimate the encoded size.
  4. Compare against the limit for your account, and for the recipient’s if you know it.

If several files are going in one message, add them up first. Five “under the limit” photos are one over-the-limit message.

Questions

What does “message exceeded maximum size” mean when the file was under the limit? The encoded message (file plus 33 percent overhead plus text and signature) exceeded the limit. Shrink the attachment to about 70 percent of the published figure or send a link.

Can I split a big file across several emails? You can split an archive into parts, but the recipient then needs to reassemble it, and many mail systems quarantine multipart archives. A shrunk file or a link is friendlier.

Does Apple Mail’s Mail Drop work with a Gmail account? Yes. Mail Drop is a feature of the Mail app, not of iCloud Mail, so it works with any account configured in Mail as long as you are signed in to iCloud. The recipient gets a download link that expires after 30 days.

Why did my video arrive looking terrible? Either the mail app compressed it automatically (iPhone Mail does this for videos) or the target size was too ambitious for the length. Shrinking to a chosen size yourself, from the original, gives a better result than letting the mail client guess. Why compressing a video twice makes it look worse explains the other half of that problem.