Strange E-mail Headers

["Tim Grogan" <timothy.grogan@grocomm.com>]

Hi all,

I've been paranoid after reading about people relaying through your e-mail
server and spamming other systems.  I've tried to lock down my system to
keep that from happening.  Today I got 2 email with these headers and I'm
wondering if I didn't catch all the opennings.

Tony Steidler-Dennison <tony@localhost.localdomain.grocomm.com>

bounce-debian-user=timothy.grogan=grocomm.com@lists.debian.org

I'm using sendmail and my domain is grocomm.com.  I also don't know Tony. A
couple of times I've received messages with my domain appended to someone
elses e-mail address.  Any suggestions would be appreciated.

Tim