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).
First, Go Down to Go North
A venerable train station turned in part into a café welcomes travelers on their way to Takasaki on the Jōetsu line in central Japan.
If you plan to go back to Echigo-Yuzawa or Niigata, though, you better plan to finish your coffee early.
For while the southbound trains at Doai station stop conveniently in front of the station building, all trains going north stop 230 ft (70 m) underground in a tunnel that can only be reached walking down 486 stairs.
While this may not be a maximum for how deep a railway station can be, there is a maximum for the amount of attachment you can send (or receive) in Proton Mail:
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 not only Base64-encoded for email transfer with Proton Mail but also encrypted, which can increase file sizes a bit.
| 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 |
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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 | 25 MB |
| Maximum individual attachment size | 25 MB |
| Maximum number of attachments | 100 |
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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.
(This is the maximum attachment size in Proton Mail updated November 2023)