Unfortunately, CDONTS was not made to work properly on Windows Server 2003. The side effects of trying to make CDONTS work with 2003 is that sometimes email will fail, or stall. When you see this happen, please let us know. Below, I have included further documentation for further details. You may want to consider changing your email method from CDONTS to CDOSYS, as the conversion process is minor.
Changing to CDOSYS