We used to be customers of Mi8 which was acquired by Apptix (also the owner of Mailstreet).
After having been a customer of Mi8 for over 8 years, we have had nothing but trouble with Apptix/Mailstreet:
1. We have constant interruptions of our service. We have at least issues every single month with activesync not working, the exchange server not working, or something like it. CONSTANTLY THE SERVICE IS NOT WORKING!
2. Apptix will sell you more service than they can actually provide. We have one very heavy exchange user with multiple folders and thousands of items in his mailbox. Although Apptix gladly charges you for multiple GB of space for mailboxes, they cannot actually provide that service! THEY CHARGE FOR SERVICE THAT THEY CANNOT OR WILL NOT PROVIDE! And when we asked for a discount in pricing, since they are clearly charging us for service that they are unable or unwilling to provide, customer service gets rude, which brings me to my next point...
3. Customer service is just rude. They will not help you with issues and the standard answer seems to be that nothing seems to be wrong on their end and that they will get back to you, which happens hours later when they admit that there was some issue on their server.
4. Pricing. Apptix is just plain more expensive than any other exchange provider. They have hidden fees and charges for everything and customer service will attempt to charge you for technical support, even if the issue is on their side! And forget about ever getting a discount, if you complain about interruptions to service. We would gladly pay their higher prices if it meant that our emails "just worked" without anybody having to worry about or troubleshoot it.
Verdict: STAY AWAY!