How are mails in the MailDepot stored, compressed, and encrypted?

How are mails in the MailDepot stored, compressed, and encrypted? How effective is the compression and how much space will a mail need?

E-mails found in the MailDepot have been compressed and encrypted when stored into the MailDepot.
The encryption method used for this is the Advanced Encrytion Standard 256 (AES 256).

The mails are compressed using GZip.
The rate at which they are compressed depends on the contents of the mail.
A mail that is mostly plain text will save much more space upon compression than a mail with attached Pictures.
Therefore it is not possible to clearly define how much space each mail will need.