Why are my files larger on ProtonMail than on my device?

When attaching files to emails, you may have noticed that they appear larger in your email than on your device. You are correct. The files size increases due to the encoding and encryption process that is necessary for your file to be sent securely on the ProtonMail system. Due to this process, the file will increase by about 1.4 times its original file size.


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  1. gaich

    What`s the size limit for attachments?
    My friend could not send me an attachment of 17MB, what size will fit and what size of attachment should I consider to send?

  2. KND

    I believe the attachment size limit is 25 MB, with encryption. Am I correct?

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