OK, I've read Massimo's posts many times about these errors being due to
communications issues and MTU's; however, in the situation like we're in now
whereby we suddenly can't send to a handful of domains (e.g. prodigy.net and
comcast.net) I understand this is likely due to escalated spam filtering on
the other end.

Since it seems to be such un ungodly hassle to even speak with anyone useful
at huge companies like these, is there nothing we can do to GWIA to allow us
to succeed where we're failing now? After all, other companies with
different email systems seem to be able to send to these companies.