hostname: naic.nasa.gov
filename: files/general_info/email-source-hints.txt
updated:  9/93 (AM)

    "Rules of Thumb" for Determining the Source of Electronic Mail
    ==============================================================

One of the most common questions is "How do I know what network my
mail is coming from?"  We present here basic guidelines for
determining where an electronic mail message came from simply by
looking at the syntax in its "From:" field.  It is important to
remember that, because of the increasing interconnection between
different networks, some addresses may incorporate aspects of more
than one of the cases listed below.  For more information, please
contact the NAIC at 415-604-0600 or naic@nasa.gov or
EAST::"naic@nasa.gov".


Case 1: Two Colons (::)
-----------------------
If the address includes "::" then it came from a DECnet network (most
likely NSI-DECnet, maybe THEnet, HEPnet, or a smaller regional net).

Sample DECnet addresses:   foo::bar::whozit     foo::bar


Case 2: Exclamation Marks (!)
-----------------------------
If the address includes a bunch of exclamation marks ("bangs" in
networkese), then its source is -- or it passed through -- UUCP (the
name "UUNET" is some- times used).

Sample UUCP Address:  foo!bar!ad!infinitum!ad!nauseum!username


Case 3 : "AT-sign" (@), Part One
--------------------------------------
If the address includes an "@" and the name of the computer it came
from includes "VM", "MVS", or "BIT", and/or if the nodename is a
single word, then its source is probably BITNET. (BITNET addresses
also tend to be all upper-case).  If the address shows up on a VAX
with JNET% at the beginning, it is definitely from BITNET.

Sample BITNET Addresses:   FOO@NMTVM    FOO@SCFMVS    LEV@DFTBIT 


Case 4: "AT-sign" (@), Part Two
-------------------------------------
If the address includes an "@" and has a multi-part nodename (or a
number for the node name) ending in .gov, .com, .edu, or something
similar, then it came from a TCP/IP ("Internet") node. (Internet
addresses are often either all lowercase or mixed-case letters.)
Also, if the address shows up on a VAX with the EXOS%, SMTP%, or EDU%
prefix, it definitely came via TCP/IP.

Sample TCP/IP Addresses:   lev@dftnic.gsfc.nasa.gov   
                           lev@128.183.112.2


Case 5: Parentheses and Colons
------------------------------
If the address includes a series of "statements" enclosed in parens,
you can be pretty sure it came through an X.400 network (e.g.
GSFCMail, NASAMail).

Sample X.400 Address:  (C:USA,ADMD:TELEMAIL,PRMD:GSFC,O:GSFCMAIL,UN:BLEV) 


Case 6: Square Brackets ("[" and "]")
-------------------------------------
If the address includes something enclosed in square brackets and/or
words separated by "/" you can be pretty sure it came through an X.25
network (e.g.  SprintNet).

Sample X.25 Addresses:   [BLEV/GSFCMAIL]    [POSTMAN]TELEMAIL/USA 

