If you are sending e-mail with a file attachment, or multiple file attachments, the total file size limit is 20 MB. If you try to send an e-mail with a final message size of over 20 MB, the e-mail will not send. FTP (file transfer protocol) may be a good alternative to use (if available) if you need to send file attachments over the 20 MB limit.
It is important to note that files that are attached to an e-mail are larger than they are on disk. This is because attachments are MIME encoded, which increases a file attachment size by 137%. If, for example, you attach a 15 MB file to an e-mail, it is possible that the final message size is over the 20 MB limit.
Based on current research, the file attachment size limitations at some other service providers are as follows: