It appears there is a problem with the Pop3Client when connecting via SSL in a 64 bit environment. Here's what I found:
My test program, compiled for "Any CPU", when run on Vista x86, successfully connects to both ssl and non ssl pop3 servers. When run on W2K3 x64, it successfully connects to non SSL pop3 servers, but does not connect to the same ssl pop3 server that was successful on the Vista machine. Instead, it receives a "Timeout Exceeded" error message.
When I compile the test program with no code changes for x86, it successfully connects in all 4 scenarios. My real code is running under the IIS process, and I am taking advantage of x64 features in other parts of my program, so running the program as x86 is not really an option at this time.
Can you take a look and let me know?