A. The size limit for incoming mail is 50MB.
With regards to outgoing mail, 40MB is the limit but it should be noted that some mail providers will reject a mail of this size. If you want to send a large file to a contact, we would recommend looking at a file sharing service instead of using email to do this.
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.