a dot in the e-mail address

From: jagadeesh-v <jag_at_getafix.cmc.net.in>
Date: Sun, 25 May 1997 14:02:19 +0500 (GMT+0500)

   This is just of my interest to know what it all is.

My friend's address is mt.hashmath_at_abb.com
I want to know "what is the meaning/significance of the '.' (dot) on the
left hand side of the '_at_' mark between 'mt' and 'hashmath'. Anybody who
is using this / knows this , please explain me the same"

Thanks
jagadeesh.v
Received on Mon May 26 1997 - 20:29:09 NZST