the user addition code needs to at least do a lookup of the
host name to see if it exists before it tries to add the
added changes to lose any spaces that were accidentally inserted into
email addresses (see bug #1223). while this wasn't really a bug, and
has code to explicitly deny email addresses with spaces in them, it
was a simple thing to add.
Backed out changed for #1223 because it was causing "oddities" that it
shouldn't have. I choose the lesser of two evils.
This is just too difficult to do; there's no concrete way to ensure
that hostnames exist with DNS servers going up and down all the time.