A. The size limit for incoming mail is 25MB.
With regards to outgoing mail, this is theoretically 50MB but many mail providers will reject a mail of this size. If you need to send an email with a large attachment, we would recommend not sending anything larger than 20-30MB.
We would also like to note that due to the process of encoding attachments in the MIME format when sending mail, the size of the email will often be significantly larger than the size of the attached file itself.