Email attachment size limits,
every provider (2026)
Most email providers cap attachments between 20 and 25 MB — and because attachments are Base64-encoded, the largest file you can actually send is about 75% of the stated limit. Here is every major provider, verified.
| Provider | Stated limit | Real max attachment* | Notes |
|---|---|---|---|
| Gmail (free & Workspace) | 25 MB | ~18 MB | Files over 25 MB auto-upload to Google Drive; recipients can receive up to 50 MB. |
| Outlook.com / Hotmail | 20 MB | ~15 MB | Larger files are offered as OneDrive shares instead of true attachments. |
| Microsoft 365 / Exchange Online | 25 MB (default) | ~18 MB | Admins can raise the cap to 150 MB per message; most tenants keep the default. |
| Exchange Server (on-premises) | 10 MB (default) | ~7 MB | Fully admin-configured; 10 MB is the long-standing out-of-the-box default. |
| Yahoo Mail | 25 MB | ~18 MB | Hard cap — no built-in cloud fallback for larger files. |
| Apple iCloud Mail | 20 MB | ~15 MB | Mail Drop sends files up to 5 GB via temporary iCloud links (30-day expiry). |
| Proton Mail | 25 MB | ~18 MB | Also caps at 100 attachments per message. |
| Zoho Mail | 20 MB (free) | ~15 MB | Paid plans raise the per-message cap; exact limit depends on the plan. |
| AOL Mail | 25 MB | ~18 MB | Same 25 MB cap as Yahoo (both operated by the same parent). |
| GMX | 20 MB (free) | ~15 MB | Higher caps are part of GMX's paid tiers. |
| Mail.com | 30 MB | ~22 MB | Slightly above the typical 20–25 MB industry default. |
| Fastmail | 50 MB | ~37 MB | One of the highest standard message-size caps among major providers. |
| Comcast Xfinity | 25 MB | ~18 MB | Typical for ISP-provided mailboxes in the US. |
| Corporate gateways (Mimecast, etc.) | Admin-set | Varies | Commonly 25–100 MB; the gateway limit overrides whatever your mail client allows. |
* Attachments are Base64-encoded inside the MIME message (+~33% size), and headers plus body text count toward the same cap — so the largest binary file that reliably fits is roughly 75% of the stated limit. Delivery is always governed by the lowest limit in the chain: yours, every relay's, and the recipient's.
Citing this table? Link to https://everytransfer.com/email-attachment-limits — it is kept current, with changes logged below.
Why "25 MB" never means 25 MB
Email was standardized in the early 1980s to move text, not files. When you attach a file, your mail client encodes it as Base64 text inside the MIME message — inflating it by roughly a third. A 25 MB cap therefore fits about an 18 MB real file, and that is before the message body, headers, and inline images take their share.
The second trap is that limits apply at every hop. Your provider, any relay or security gateway in between (Mimecast, Proofpoint, corporate Exchange), and the recipient's server each enforce their own cap — and the smallest one wins. This is why a message that leaves your Fastmail account fine can bounce off a client's 10 MB on-prem Exchange hours later.
The reliable way around all of it: send a transfer link instead of an attachment. The email carries a few bytes of URL; the file — whether 100 MB or 100 GB — travels outside the mail system entirely. Our guide to sending files too big for email compares every method.
Attachment limit questions, answered
What is the maximum attachment size for Gmail?
Gmail allows attachments up to 25 MB per message. Because attachments are Base64-encoded, the largest real file that fits is roughly 18 MB. Anything larger is automatically uploaded to Google Drive and sent as a link instead.
Why does my 20 MB file fail even though the limit is 25 MB?
Email attachments are Base64-encoded inside the MIME message, which inflates them by roughly 33%. A 20 MB file becomes about 27 MB of encoded data — over the 25 MB cap. As a rule of thumb, the largest file you can actually attach is about 75% of the stated limit.
Why do email providers limit attachment sizes at all?
Three reasons: every relay server in the delivery chain has to buffer the full message, mailbox storage fills quickly with large duplicated attachments, and SMTP was never designed as a file transfer protocol. Limits keep email fast and reliable for everyone.
What happens if I send a file that is too big?
Either your provider rejects it immediately, or a receiving server bounces it back with a "message size exceeds limit" error — sometimes minutes later. Gmail and Outlook instead auto-convert oversized attachments into Google Drive or OneDrive links.
Do attachment limits apply to receiving email too?
Yes — and this is the most common gotcha. Delivery is governed by the lowest limit in the chain: if you can send 50 MB from Fastmail but the recipient's Exchange server accepts 10 MB, the message bounces. You never know the recipient's limit in advance.
How do I send files bigger than any email limit?
Upload the file to a transfer service and email the download link instead. The link weighs a few bytes, so it always arrives — and the file itself can be gigabytes. EveryTransfer creates such links free, without an account, with optional password protection and download tracking.
Changelog
- July 2026 Initial publication — 14 providers verified against current documentation.
File too big for email?
Upload it to EveryTransfer, email the link instead — free, no account, with password protection and download tracking built in.
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