This is going to be hard to explain, so please bare with me. I have my MU on a subdomain, blog.abc123.com. The default email that I chose during installation was admin@abc123.com. I didn't get the initial email for my info. After that, when I make a new blog under a different name, I get an email. But, when I try to send a password reset to admin@abc123.com, I never get one. But, what I do get is an error back to my email account that says:
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
admin@abc123.com
retry timeout exceeded
Thats the end of it.^
I'm not sure if this is a problem with MU or with my host/cPanel. But, I'm leaning towards my host.