In fact, I too am noticing a high traffic on the SmarterMail server (both in upload and download).
More or less, I have about 30GB to 180GB of UPLOAD (towards users) per day.
Calculating that in the SmarterMail statistics the sum of SMTP, IMAP and POP3 does not exceed 10-15GB (as you can see in the following image), I deduce that the rest of the traffic is generated by MAPI / EWS or by EAS (the latter is probably the culprit).
It would be interesting to understand WHAT generates this exaggerated traffic, because if EAS actually causes so much traffic with few users (I have about 40), it will soon become a problem as the number of users grows ...
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)