Thanks for that, Athanasius!  Well explained.

I've been using MIME::Lite for years without problem, but only on a Linux server.  This is the first time I've used it on Windows.

If this is a server problem (as an Anonymous Monk suggests), then can I expect similar problems with other mail modules?  I would have thought so.

(My ISP (Vodafone NZ) is getting out of the email game, due to them not being able to handle spam quantities, and they probably aren't officially supporting email sending anymore, so maybe their server is a bit (or even a byte)...stuffed, due to lack of maintenance.  I don't need a long term solution for this though.)