We have been seeing a similar problem with Quaramed’s EDM product. In our case, their interface thinks it is getting a partial message and won’t ACK until it gets the whole thing. These are always 1458 characters which is the usual packet size for a system set up to send 1500 as the max size minus some encoding characters. It doesn’t happen on all 1458 message and when i bounce their side, the same message that wouldn’t go thru now goes thru without a problem. We looked for EOF characters, extra ^M etc and found nothing which accounts for why they go thru once the connection on their side is bounced. They have tried a few things but no success. The last I heard, they were looking into a malformed .exe file. I hope they find it soon! if we do, I’ll try to let you know to see if it may be an avenue for you to pursue.