Message-Id: <199609261650.MAA14985@CS.UTK.EDU>
Date:        Thu, 26 Sep 1996 18:36:32 +0200
From: Eric Thomas <ERIC@VM.SE.LSOFT.COM>
Subject:     Maximum userid/hostname lengths
To: drums@cs.utk.edu

What are the  current maximum values for local-part and  hostname in SMTP
mail? These were defined as 64 +  64 by RFC821, but I'm sure the hostname
would have  been redefined in  a more  appropriate standard, and  I'm not
sure the  local-part was  ever changed  (not in  1123 anyway).  Also, are
there known cases where values significantly larger than 64 are used? I'm
aware of the fact that X.400 gateways routinely exceed this limit.

I know what values are safe, and  it's easy to implement mail software so
that arbitrary  lengths are  supported, so it's  normally a  non-issue. I
just have a customer who wants to  size a database field so that there is
a 100% guarantee that any SMTP address  will fit. My take is that this is
unrealistic, unless  you're willing  to spend  the disk  space on  a huge
value. Hostnames  are unlikely to  ever get significantly longer  than 64
bytes, because people  are going to have  to be able to type  them, but I
can see gateways stuffing more  and more information into the local-part,
not to mention %-hacks, etc. Send  an MCI address through a X.400 gateway
and back and I wonder how many miles it takes up.

  Eric