Email attachment size limits: every major provider, and why your file still bounces

For most people the practical ceiling for an email attachment is 20 to 25 MB per message, and that number covers every attachment plus the message text, after encoding. Gmail, Yahoo and Proton Mail let you send 25 MB; Outlook.com and iCloud Mail stop at 20 MB; a default Microsoft 365 mailbox allows about 35 MB. Because attachments grow by roughly a third when they are encoded for sending, the largest single file you can reliably send through a 25 MB service is closer to 18 MB. Anything bigger should travel as a link or through a direct transfer, not as an attachment.

The limits, provider by provider

These figures come from each provider's own help or service-description pages at the time of writing (October 2026). "Send" is what your account will let you send; "receive" is the largest incoming message your inbox will accept.

A few details the table cannot hold:

• Gmail documents the 25 MB sending limit in its help centre. The 50 MB receiving limit was announced by Google in 2017 and Google said sending would stay at 25 MB. If you try to attach more than 25 MB, Gmail uploads the file to your Drive and inserts a link instead, so check the recipient can open it.
• Microsoft 365 limits depend on the client as well as the mailbox. Microsoft's service description lists Outlook on the web at 112 MB and Outlook for iOS and Android at 33 MB per message even when the mailbox allows more, and it notes that Outlook on the web deliberately caps you 25% below the configured limit to leave room for encoding. Older on-premises Exchange servers are often set much lower; Microsoft's own Outlook help page quotes 10 MB as a typical business default.
• iCloud Mail applies 20 MB in both directions. Mail Drop raises the ceiling to 5 GB by sending a link instead of the file, with a rolling 1 TB Mail Drop allowance and a 30-day expiry.
• Zoho does not offer Huge Attachments on its free plan, and administrators on paid plans can set tighter limits through mail policy.

Why a 19 MB file can bounce from a 25 MB account

Email was designed for 7-bit text. A photo, PDF or zip is binary data, so before it leaves your outbox it is wrapped in MIME and converted with base64 encoding, which represents every 3 bytes of the file as 4 text characters. That alone adds 33%. Line breaks inserted every 76 characters add a little more, and the message headers, the HTML and plain-text versions of your message, signatures with logos and quoted earlier replies all count too.

Microsoft is unusually direct about this. Its Exchange Online limits page says messages that leave Microsoft's data centres are "subject to an additional 33% translation encoding increase", which is why a 150 MB internal limit becomes 112 MB for external mail. Proton's help page likewise warns that encoding makes attachments "a bit larger" than the originals.

Worked example

You want to send three files from Gmail: a 9 MB PDF and two 4.5 MB photos, 18 MB in total.

1. Raw size: 9 + 4.5 + 4.5 = 18 MB.
2. After base64: 18 × 4/3 = 24 MB.
3. Add line breaks (about 2.6%), headers, the message body and a quoted thread: roughly 24.7 to 25 MB.

That is right on the line. Some services count the raw file size in the compose window and only fail at the server; others count the encoded size up front. Either way, treat about 75% of the stated limit as your real budget for files: around 18 MB for a 25 MB service and 15 MB for a 20 MB one.

The recipient's limit matters as much as yours

An email passes through at least two mail servers: yours and the recipient's. Each has its own maximum message size, and the smaller one wins. If you send a 30 MB message from a Microsoft 365 mailbox to someone on iCloud Mail, your server accepts it and the message leaves, then iCloud refuses it because it is over 20 MB. You get a bounce (a non-delivery report) minutes or hours later, often with a cryptic line such as "552 message size exceeds fixed maximum message size".

This catches people out in three common situations:

• Sending from work to a personal address. Your company may allow 35 MB or more, but Outlook.com and iCloud stop at 20 MB.
• Sending to companies, schools and government offices. Many organisations set limits of 10 MB or lower, and some strip certain attachment types (such as .zip or .exe) entirely, regardless of size.
• Forwarding. Forwarding a message with attachments and adding another file can push a thread over the limit even though each piece was fine on its own.

Because you cannot see the recipient's server setting in advance, anything above about 10 MB going to an unfamiliar organisation is safer as a link.

What to do when the file is too big

There is no single right answer; it depends on how big the file is, how quickly it needs to arrive and whether the recipient will download it right away. Work down this list.

1. Make the file smaller, if that is genuinely possible

Zipping helps with documents, spreadsheets, CSV exports and folders with many small files. It does almost nothing for JPEG photos, MP4 videos or MP3 audio, which are already compressed. For a scanned PDF, re-exporting at a lower image resolution often cuts the size by more than half. Our guide to zipping files covers when compression is worth the effort and how to do it on each operating system.

2. Use your provider's own link feature

Gmail's Drive links, Outlook's OneDrive attachments and Apple's Mail Drop all keep the familiar "send an email" workflow while moving the file itself outside the message. They work well when the recipient may download later, and they are the better choice if you need the file to stay available for days. The trade-offs: the file is stored on the provider's servers, sharing permissions can trip people up (a Drive file shared only with your organisation will not open for an outside client), and the recipient may need to sign in.

3. Send a link from a transfer or cloud service

Services such as WeTransfer, Dropbox or Google Drive let you upload once and send a link that works for a set period. This is the most practical route for "they will download it tomorrow" situations and for sending the same file to many people. Our overview of options for files too big for email compares them, and if you send deliverables to clients regularly, see how to send large files to clients.

4. Transfer directly while both of you are online

If the recipient is available now, a live peer-to-peer transfer avoids both the size cap and the upload-then-download wait. TransferFiles.net works this way: you open the page, pick the files, and share the link or short code; the recipient opens it and the file streams from your browser to theirs, encrypted with WebRTC's built-in DTLS. Files are not uploaded to or stored on a server, and we impose no size limit. The catch is that both browser tabs must stay open until the transfer finishes, and there is no link that works later once you close the tab. For asynchronous delivery, a cloud link is the better fit.

5. Split the file, as a last resort

Archive tools can split a large file into numbered parts small enough to email one by one. It works, but the recipient has to collect every part and rejoin them with a compatible tool, and one missing part ruins the set. Reserve it for cases where links are blocked by policy.

Choosing quickly

Sources

• Google: Attachment size limits in Gmail
• Google Workspace Updates: Receive emails of up to 50MB in Gmail
• Microsoft Support: Send large files with Outlook
• Microsoft Learn: Exchange Online limits
• Yahoo Help: Message size limits in Yahoo Mail
• Apple Support: Mailbox size and message sending limits in iCloud
• Apple Support: Mail Drop limits
• Proton Support: Attaching files to a message
• Zoho Mail Help: Attachments in emails
• Zoho Mail Help: Huge Attachments