That configuration should be more than ample for your Users and Email Volume. We have about 300 domains and 3000 users (most of which are IMAP) with a daily email volume of 60,000 Incoming/30,000 Outgoing messages running on the following:

 

Quad Core X3450 - 2.66Ghz

Windows Server 2008R2 (will be upgraded to 2012R2 next month)

16GB ECC RAM

4xSeagate Constellation ES.3 SAS Drives (Raid-10)
Dell SAS6/iR Raid Controller
 

Very similar to your configuration (with half the RAM and physical HDD) and we still have plenty of headroom to grow (we rarely peak over 10% CPU).

 

Although we aren't running SSD drives on this server, we run them on our SANs and in our ESXi boxes with much success. They are as reliable as traditional Enterprise HDDs and we use them without hesitation for Web Servers. Personally I'm still too overly cautious to run them in heavy I/O environments such as for SQL Servers and Mail Servers, but many others here have used them successfully in their Smartermail installations without trouble or complaint .

You are probably going overboard on the memory but it's not a big deal. I'd look into a better RAID adapter than the H200. I don't know the Dell RAID controllers as well as I do HP offerings but it looks like the H200 is older and a low performance model. Odds are the SSDs will tax that adapter. Spend a little more on a better RAID adapter with cache and you'll see much better performance. It might not matter for mail operations but for backup processes it will make a difference. The only other item I'd do some homework on is the SSD performance and compatibility in a RAID environment. Unlike typical hard drives there are big variations in performance among the SSD vendors. Also, if you're doing hot plug drives and have the capacity, get a fifth drive as a hot spare, SSD or not!

 

If you haven't considered it, look into virtualizing the server using Windows 2012 R2 Hyper-V or VMware. Makes life a whole lot simpler for backup, restore, migration, and the like. Bond your network adapters for fault tolerance and better throughput. Again, doesn't really affect mail operations but for big data throughput purposes (network backup for example) it really reduces the maintenance windows and such. Good luck.

 

Matt

Thanks for your feedback guys