Don’t like to play guessing games with important files? Wondering how big secure and encrypted file attachments can be in Proton Mail? Find here the maximum attachment and message size in Proton Mail ⤓ (both for sending and receiving).
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This Is the Maximum Attachment Size in Proton Mail
Sending from Proton Mail
When you send an email that includes attachments,
- Proton Mail allows for a size of 25 MB in total.
- You can add up to 100 individual files.
Together with the message contents and possibly header lines, attachments are Base64-encoded for transfer and encrypted. Both can increase the file sizes a bit.
Their word: Proton include information about size limits in their Proton Mail documentation.
| Aspect | Interface | Size Limit |
|---|---|---|
| Proton Mail total message size | Web, Proton Mail app, Proton Mail bridge | 25 MB |
| Maximum individual attachment size | Web, Proton Mail app, Proton Mail bridge | 25 MB |
| Maximum number of attachments | Web, Proton Mail app, Proton Mail bridge | 100 |
Looking to send larger files?
How to Share Large Files with Proton Drive (Proton Mail Workaround)
Sending to Proton Mail
When you send an email message to a Proton Mail address, the same limits apply.
You can send messages up to 25 MB in size and up to 100 files attached to each message.
Note that Proton Mail considers the size of the encrypted message delivered to the Proton Mail recipient. If your email is not encrypted with the user’s PGP encryption key, Proton Mail will encrypt it, which can increase its size.
| Aspect | Size Limit |
|---|---|
| Total encrypted message size | 50 MB |
| Maximum individual attachment size | 50 MB |
| Maximum number of attachments | 100 |
Maxing out on Proton attachments?
Tips help fuel these email and tech how-tos.
This Is the Maximum Attachment Size in Proton Mail: FAQ
How much will the attachment size increase with Proton Mail encryption?
This can vary depending on the data encrypted and the size of the file.
For small files, a noticeable increase is possible with added meta-data while files that are several 100 MB in size will not increase in size.
A file of 20 MB might typically increase by 0.5% to 21 MB.
Note that Base64 encoding, which is necessary to transfer arbitrary data using email, will add 33% to a binary file’s size.
Looking for the largest emails? How to Sort Proton Mail by Size
Looking to free up space? How to Empty “Trash” and “Spam” in Proton Mail
(First published November 2023, last updated August 2026)