Erratic Connections to Email Servers

[MWE]

I use Outlook2000 for all email activity. I connect to
several different email servers daily. Everything works
fine except for one account (hosted by register.Com).
After connecting to the email server, incoming mail works
fine, but outgoing mail is "strange". Mail in my Outlook
Outbox created in a previous session goes out fine. But
mail in that same Outbox created during the current
session "just sits there". The workaround is to close the
session after completing new and replies and restart
Outlook. Register.com support admits that there are
problems with Outlook and their server, but this smells
more like something at my end.

Any Thoughts?

Thanks