Reference
Gmail attachment size limit, sending and receiving
Gmail allows attachments up to 25 MB when sending and accepts messages up to 50 MB when receiving, including all attachments. Because attachments are encoded for transport, a file of roughly 18 MB on disk can exceed the 25 MB send limit once encoded.
| Sending | 25 MB total message size, attachments included |
|---|---|
| Receiving | 50 MB total message size, attachments included |
| Encoding overhead | Roughly 33 per cent added by base64 encoding in transport |
| Practical send ceiling | About 18 MB of files on disk |
| Over the limit | Gmail offers a Drive link instead of an attachment |
Why a file under 25 MB still bounces
Mail transport encodes binary attachments as text, and that encoding adds roughly a third to the size. A 20 MB file on disk arrives at the limit check as around 27 MB, which is over the sending ceiling even though the file properties say otherwise.
The same arithmetic explains why forwarding a chain with several inline images fails when each individual image looked small. The limit applies to the whole message, quoted history and inline content included.
What administrators can and cannot change
The 25 MB send limit is a Gmail platform limit and cannot be raised in the Admin console. What an administrator can change is the receiving path: content compliance rules and gateway settings can reject messages well below 50 MB.
If large files move between the same parties regularly, a shared drive folder with link sharing is the supported answer. It also removes the duplicate copies that attachments create in every recipient's mailbox.
What we see that others don't say
Because encoding overhead is applied before the limit check, the honest guidance to give users is 18 MB of files rather than 25 MB, which removes almost all of the failed send tickets we see on this issue.
What this doesn't cover
- These are Gmail limits; a receiving server elsewhere may impose a smaller one and reject the message anyway.
- Third-party mail gateways in front of Gmail apply their own size limits that we cannot see from your tenant.
Questions we get asked
- Can a Google Workspace admin increase the 25 MB attachment limit?
- No. The 25 MB sending limit is a platform limit with no Admin console setting. Sharing a Drive link is the supported route for larger files, and Gmail offers it automatically when an attachment is too large.
- Why does Gmail say the message is too large when the file is 20 MB?
- Transport encoding adds roughly a third to the attachment size, so a 20 MB file is measured at about 27 MB against the 25 MB sending limit. Quoted history and inline images count towards the same total.
How this page is verified
Reviewed by Pearl Lemon Cloud migrations desk, Google Workspace migration engineers. Last checked .
- Limits verified against Google's published Gmail sending and receiving limits at the review date.
- Encoding overhead calculated from base64 transport encoding, which expands binary content by about a third.
Sources you can check
Related pages
Users hitting attachment limits every week?
We replace the attachment habit with shared drive links and a mail policy that states the real ceiling, so the failed sends stop rather than get retried.