Currently, I'm using SmarterMail 5.5 Enterprise as an email server for multiple domains (~30 total users). My situation is that I need exchange-like behavior for 2 or 3 users. And, by exchange-like behavior, I mean syncing of email, contacts, and calendar for Outlook 2007, Apple Mail, and iPhone. For these 2 or 3 users, I've narrowed it down to the following 3 options:
1. SmarterMail 6.x Exterprise with ActiveSync Add-on (would cost $200/year, but could add up to 25 user accounts)
2. Exchange 2010 Standard (would require the purchase of Windows Server Standard, Enterprise, or Datacenter, because I currently only own licenses for the Web edition.)
3. Google Apps Premier
The benefit of option 1 is that I wouldn't need an MTA/email gateway...so that's the option that I'm leaning towards. However, I've read in several articles indicating that utilizing an MTA is a best practice. So here are my questions:
1. Any advice/suggestions (not limited to the options I mentioned)?
2. What software should I use for the MTA (can be windows or linux)? Is it possible to configure user-specific email routing at the MTA level?
3. Even if I go with SmarterMail, should I stand up an MTA anyways? Why?
4. Any suggestions for redundancy/failover in case the email server goes down?
I'm open to any Linux and/or Windows solution, as I'm planning to virtualize a couple of servers. Thanks in advance.