e-mail strangenesses

[http://dummy.us.eu.org/robert (Robert)]

To: http://www.sonic.net/~support

When I try sending mail via your SMTP servers, my mail doesn't work.  If I
ssh to shell.sonic.net and use "mail", it works fine.

The addresses I'm having problems with are:

http://dummy.us.eu.org/robert
http://dummy.us.eu.org/robert

(both of these domains point to my static IP).  So, if I ssh to
shell.sonic.net and say

$ mail http://dummy.us.eu.org/robert
Subject: test

test
.
Cc:

it works fine.  If I send the mail to http://dummy.us.eu.org/robert through
my