I wish I could +1 Joe's comment because it pretty much sums up AOL's service attitude.
Having said that, there is no reason that SmarterMail should specifically address any AOL interconnection or interaction issues with their products. There are established protocols for every internet interaction and connection, and AOL must follow them, like everyone else, if they expect to continue to deliver e-mail.
So, my only remaining question is how are you connected to the Internet? Speed? Service reliability, etc.
I ask because a very large library, in a major east coast city, was having issues similar to your a couple of years back and I worked to help them resolve the problem.
The issue turned out to be a bad CORE ROUTER in their provider's network, which was literally dropping connections in mid-stream when the MTU exceeded 1492. While an MTU of 1492 used to be the "standard" in e-mail connections, at one point Comcast figured out that by pushing the MTU up to 1500, once the connection between two MX servers was established, they could gain something like 250,000 internet minutes of connectivity per day because of the volume of e-mail traffic they are pushing.
I am not stating that is the same issue which is causing your problem, but it certainly sounds like this is either an issue with your hardware or the route that the e-mail data is taking between you and AOL.
Since you have not stated that this happens with other MX providers, only with AOL, then it sounds like an issue with the route that the e-mail traffic is taking between you and AOL.
This will be VERY hard to diagnose and troubleshoot. You can start with a traffic monitor and have it capture all traffic, to and from, AOL - down to the packet level, and see what's going on. Remember, that is going to give you access to the actual data contained in the messages, so be very careful with that data and who you share it with because some of it could contain confidential information.
You can also look at the IP addresses which are used in the AOL traffic and do TRACERTs to those addresses, checking to see if the traffic fails at one or more points along the route.
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