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E-mails size are calculated bigger than actual size

7464247 shared this question 9 months ago
Need Answer

I found out that e-mail attachments' size are treated bigger than their actual size. For example, I need to send an e-mail with an attachment, the attachment's actual size is 14.5 MB. However, after I sent the mail, the server of mailbox.org calculated the attached file is 19.9MB! All my e-mail are bigger than their actual size! This is quite not fair! We know that mailbox.org needs users to upgrade their plan to earn money, but the way of making files size bigger than their actual size cannot be accepted! Please calculate the size of attachments normailly.


An attached file's actual size:

d1a71368ccd21fdf5dccab1a6798f832

The file's size showed on the server:482a79d69be0d74ce9d53a8c48a8cdce

Best Answer
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Please don’t jump to conclusions. You’ll only get wet.

“Note that all these size limits are based, not on the original file size, but the MIME-encoded copy. The common Base64 encoding adds about 37 % to the original file size, meaning that an original 20 MB file could exceed a 25 MB file attachment limit.[4] A 10 MB email size limit would require that the size of the attachment files is actually limited to about 7 MB. ” – Wikipedia on email sizes

There is a future 2,4 % discrepancy for historical reasons. 1 Megabyte (decimal; 1000 kB / 976,5 kiB) versus 1 Mebibyte (binary; 1000 kiB / 1024 kB) as both systems historically used the unit “MB”. Megabyte nowadays is MB while Mebibytes is MiB but many systems, like Mailbox and Windows, use the historical MB unit when they mean MiB.

Everything is technically correct; which is the best kind of correct.

Comments (3)

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1

Please don’t jump to conclusions. You’ll only get wet.

“Note that all these size limits are based, not on the original file size, but the MIME-encoded copy. The common Base64 encoding adds about 37 % to the original file size, meaning that an original 20 MB file could exceed a 25 MB file attachment limit.[4] A 10 MB email size limit would require that the size of the attachment files is actually limited to about 7 MB. ” – Wikipedia on email sizes

There is a future 2,4 % discrepancy for historical reasons. 1 Megabyte (decimal; 1000 kB / 976,5 kiB) versus 1 Mebibyte (binary; 1000 kiB / 1024 kB) as both systems historically used the unit “MB”. Megabyte nowadays is MB while Mebibytes is MiB but many systems, like Mailbox and Windows, use the historical MB unit when they mean MiB.

Everything is technically correct; which is the best kind of correct.

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1

Thank you for correcting my mistake caused by missing knowledge about "The common Base64 encoding adds about 37% to the original file size, meaning that an original 20MB file could exceed a 25MB file attachment limit". I didn't know that before. Just because I have never encountered such problems when I was using Gmail. Gmail limits attached to 25MB, however sometimes I could even send attachments that a little bigger than 25MB. I think maybe that's the "smart" way of google doing business.


I know about 1000kib/1024kb problem, I got used with 1MB=1024kb in computer world, and I believe that should be the correct way to declare capacity of a HD or whatever.

Anyway thank you for let me know "Base64 encoding adds extra size".


Sorry for the emotional "conclusion".

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1

This is completely normal and is due to the way files are encoded when they are sent by e-mail. The attachments actually do take up more space when they're attached to an e-mail.


If you're interested in the technical details you can read more here:

https://en.wikipedia.org/wiki/Base64#MIME