One question we often get asked when talking to customers contemplating an Exchange upgrade or a switch from a competitor’s mail system is, "how many users per server can Exchange handle?" Nowadays, that’s an open question - it very much depends on what kind of users you have, what kind of storage you’re using and how powerful your servers are. When Exchange 4.0 was released in 1996, a decent server might have had 256Mb of RAM and a 90MHz Pentium processor, with maybe a handful of GBs of SCSI disk in the box and possibly a DAT tape drive. Users’ mailboxes might have been in the 10-20Mb size range, and the average user sent or received only a small amount of email per day.
 
At that time, server sizing was pretty much a function of how much computing horsepower you could afford - the CPU power, disk size & speed and memory capacity available (along with the all-important user profile) would determine the number of users per server, and arbitrary decisions would be made about maximum message sizes, mailbox size etc. Now, it’s possible to buy even mid-range servers that will cope with many thousands of users, and the bottleneck has moved down to the storage level in many instances as user mailboxes have grown in size and we send and receive far more mail, and many larger messages too.
 
We’d be interested in hearing anecdotes about particularly unusual messaging environments you might have - how large do your servers grow? What’s the biggest mailbox you’ve ever seen (assuming you’re not restricting with quotas)? How much data does your total Exchange system manage? What’s the biggest single database - etc, etc... you get the picture.
 
Some factoids to get you started...  if you have anything along these lines, please post a comment:
 
- One customer (who is part of the Exchange Technology Adoption Program) sets no limit on message sizes internally - and one time saw a single message with attachments totaling 2.4Gb in size! (which Exchange delivered! - the recipient’s mailbox quota was instantly blown apart though...)
- The largest single Exchange 5.5 Public Folder Information Store I’ve come across was 800Gb in size
- There’s a limit of 1,000 Exchange 2000/2003 servers in an org - has anyone come close, or hit that limit?
- One customer deploys around 250,000 Exchange users per server and has over 9,000,000 users in total (you guessed it, they’re an ISP)
- The most heavy user of public folders in the world (that we know about) has about 1,500,000 public folders containing around 8Tb of data
 
So come on: let’s hear your war stories - post a comment with your amazing data :)
 
- Ewan Dalton