Exchange 2010 (on a SBS 2011 server) is giving me nightmares. Incoming connections on port 25 are taking forever (if they connect at all). It's random. It's internal and external. It's even happening from the server, itself, when I "telnet 127.0.0.1 25"
Packet sniffing shows that the TCP handshake is happening instantaneously. The server, then, MAY send the 220 response or it may not. If it does, it can be instantaneous or it can be up to 60 seconds later. Once the 220 is sent, the rest of the transaction happens quickly. This is causing numerous issues with incoming email.
I have turned off tarpit. I have uninstalled (for troubleshooting) the Trend Micro WorryFree 8 antivirus. RAM usage (immediately after a reboot, anyway) is fine. CPU usage is less than 5%. Disks aren't grinding away. All patches, updates, roll-ups, service packs, etc are installed on the machine. Event logs are clean. I've set "MaxAcknowledgementDelay" to 0 on the receive connector.
The frustrating thing is that even telnet to localhost is erratic. It will work, then not work, then be slow, then not work, then work fine... all within 5 minutes.
I'm at a loss on this one. Does anyone have any other ideas?
