Email attachment size limits by provider (and how to send large files)

Every email provider caps how large an attachment can be, and the caps are lower than most people expect. The number a provider advertises is also not the number that actually applies, because attachments are encoded for transit and the encoding adds roughly a third to the file size. The real ceiling is set by the receiving server as much as the sending one, so a file that sends fine from one provider can bounce at another.

Email attachment size limits by provider

The limit that matters is whichever is smaller: the sender's outgoing cap or the recipient's incoming cap. A message has to clear both, so the lower of the two wins. These are the published limits for the major consumer providers, and they cover the recipient side as well as the sender side unless noted.

Business and self-hosted mail can differ. Microsoft 365 defaults to 25 MB but an administrator can raise it to 150 MB, and a company running its own mail server sets its own ceiling. The consumer figures above are the safe assumption when the recipient is unknown, since a file that fits Gmail and Outlook fits almost everywhere.

Why the limits exist and what counts toward them

Attachments are not sent as raw binary. Email was designed to carry plain text, so a file is encoded into text with Base64 before it travels, and that encoding inflates the data by about 33%. A 20 MB file becomes roughly 27 MB on the wire. The provider's limit applies to the encoded size, which is why a file that looks comfortably under the cap can still be rejected.

The practical effect is a gap between the advertised number and the usable one. A 25 MB limit holds a real file of around 18 MB once encoding is accounted for, and a 20 MB limit holds about 14 MB. Treating the headline figure as the true ceiling is the most common reason a send that should have worked bounces back.

The limits themselves exist because large attachments are expensive for providers to store and relay, and because multiplying a big file across many recipients strains the receiving servers. Storing one shared copy and distributing a link is far cheaper than storing a full copy in every recipient's mailbox, which is exactly what the workarounds below do.

How to send large files

When a file is over the limit, the answer is to send a reference to the file rather than the file itself. The recipient gets a link, the file lives in storage, and the email stays small enough to deliver. Three approaches cover almost every case.

• Share a cloud-storage link. Upload the file to Google Drive, OneDrive, Dropbox, or iCloud, then paste a share link into the message. Gmail and Outlook do this automatically when a file exceeds the limit, and it keeps the email tiny regardless of how large the file is.
• Use a file-transfer service. Tools like WeTransfer, Smash, or Send Anywhere upload the file and email a download link, with no recipient account needed. They suit one-off large transfers, often handle several gigabytes, and expire the link after a set period.
• Compress the file into an archive. Zipping a file, or several files, shrinks the total and bundles everything into one attachment. This helps most with documents and already-uncompressed data; media that is already compressed, like a JPEG or an MP4, barely shrinks.

The link approach has a quieter benefit beyond fitting the limit. A linked file can be updated, revoked, or tracked after the email is sent, while an attachment is a frozen copy sitting in an inbox forever. For anything that might change or that should not circulate indefinitely, a link is the better default even when the file would have fit.

How to send large videos

Video almost never fits as an attachment, because even a short clip in modern quality runs well past 25 MB. A minute of 1080p video is commonly 50-100 MB, and 4K is several times that. Attaching it directly is rarely an option, so video is the clearest case for sending a link.

• Upload to a video host and share the link. YouTube (as an unlisted or private video), Vimeo, or Loom give the recipient a player that streams rather than downloads, which is usually what they want anyway. This is the smoothest option for anything meant to be watched.
• Use cloud storage or a transfer service for the raw file. When the recipient needs the original file rather than a stream, for editing or archiving, a Google Drive or Dropbox link, or a WeTransfer send, delivers the full-quality file without touching the attachment limit.
• Compress or trim before sending. Lowering the resolution, shortening the clip, or re-encoding to a more efficient codec can bring a borderline file under the limit. This works for a short, low-stakes clip, though for most video a link is simpler than fighting the file size.

FAQ

Bottom line

The working rule is simple: keep attachments under about 20 MB of real file size, and send anything larger as a link. The providers all sit between 20 and 25 MB, encoding overhead eats into that, and cloud-storage links or transfer services handle whatever does not fit without the recipient ever hitting a limit.

This applies to manual, person-to-person email. Sending attachments programmatically, through a transactional email API, follows the same physics but with the provider's own per-message ceiling, so large files belong behind a hosted link there too. Lettr's attachment handling documents those limits for API sends, and a free account covers the common case of a receipt or report with a modest PDF attached.