Mjulian/base64 mail enlarging

When sending an email, the attachment is converted from binary to text using a base64 encoding. Thus the email attachment sees its own size increased by more or less a 35% (more than that when dealing with 70M and more files).

If the user sets a mail size limit to the postfix configuration, and he tries to send an attachment whose size is more or less close to that limit, postfix will reject that email. That will lead the user think that something is working wrong.

On the other hand, we are accepting larger emails than the user said.

In my opinion, as the Zentyal UI set a 100M as a max value for the max mail size, we should consider usability first.