What frustrates me is that there is a very common error naive programmers make when doing this kind of thing. I think it is a strong possibility that is the issue. I have brought it to their attention. No response, of course.

It is this simple: when you connect to another mail server, it can return a code indicating it is busy and you should try again later. Naive and lazy programmers either don’t know, don’t care, or are just too lazy to write the extra code that would try again.