For many years we've had a few hundred users on a SmarterMail server.  The business types are varied... photographers, real estate, home products manufacturer, insurance, legal, public relations consultants, etc.  Customers have come and gone, but all tend to fit a particular bandwidth profile.  Access is a mix of Outlook and similar, Webmail, and mobile devices (POP/IMAP).  Daily traffic looked like this, with very few exceptions (a daily graph from 3 weeks ago).  
  

Last week we added the first 55 users of a new client who will be migrating over in phases.  These users are almost exclusively using Webmail and EAS (mobile).  Message volume itself-- by count and GB-- is typical of our average users.  The difference is, nearly all of these 55 new mailboxes are using Webmail and EAS, not POP/IMAP.  Here is what the week's bandwidth consumption looks like now.  (Fri/Sat/Sun are inbound migration and can be ignored).  Notice the outbound traffic staring Monday morning.

And here's a closeup look of the past day.


Again, I stress that message volume when measured by quantity and bytes, is within the average of the hundreds of other users on this server.

Since the only difference seems to be the predominant use of Webmail and EAS, instead of POP/IMAP, my first assumption is Webmail and EAS consume inordinately large amounts of bandwidth.

This is a huge concern, because we've gone from hundreds of users consuming 1-2 Mbps on average, to just 55 more users consuming 20-100 Mbps.  This huge spike is attributed to only those 55 users.  Extrapolating this out to the additional 1320 users (same customer) migrating next week who will also be Webmail + EAS, we could be looking at saturating a full Gigabit connection.  On a mail server with fewer than 2000 users, that is insane!

This is HUGELY out of profile.  Our Exchange Server has just under 1,000 users and its bandwidth profile looks like this:  (this segment uses solarwinds, so the chart appearance is different from mrtg)

So Exchange Server-- which is all MAPI and EAS-- is fitting nicely within 10 Mbps for nearly 1,000 users.  But SmarterMail with 55 additional users on Webmail and EAS has skyrocketed by comparison.

Anyone else having similar experiences when EAS is added and users prefer Webmail instead of POP/IMAP?