See also:
Exchange mail server 2016

Total installation Server 2016 and Exchange

Click on photo to enlarge

The 2 clients are connected to the server.
The Exchange Mailserver is installed.
Outlook accounts are configured.
And the attachments of the mail are limited to 2 mb
So that an error message is given because of that 4 mb attachment

And this result can only be achieved if all the above has been done properly

The mail from Bert to Ernie of 4 MB is refused

The message to be sent exceeds the message size set for this user

Security Policy?
Avoid steganography