+++ This bug was initially created as a clone of Bug #171838 +++

Description of problem:
When an external SMTP session is established, and an address of
"xxx" is specified on the MAIL FROM: line, sendmail
blindly accepts this as valid.  Note that "xxx@localhost" is rejected by
sendmail.

Version-Release number of selected component (if applicable):
sendmail-8.13.1-2

How reproducible:
Always

Steps to Reproduce:
1. from a remote host, telnet host 25
2. EHLO foobar.redhat.com
3. MAIL FROM: <xxx>
  
Actual results:
220 vaccine1.NoDak.edu ESMTP Sendmail 8.13.1/8.13.1; Wed, 26 Oct 2005 16:17:42 -
0500
EHLO nate.cc.ndsu.nodak.edu
250-vaccine1.NoDak.edu Hello nate.cc.ndsu.NoDak.edu [134.129.106.131], pleased 
to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE 26214400
250-DSN
250-AUTH GSSAPI DIGEST-MD5 CRAM-MD5
250-DELIVERBY
250 HELP
MAIL FROM: root@localhost
553 5.5.4 root@localhost... Real domain name required for sender address
MAIL FROM: root
250 2.1.0 root... Sender ok

Expected results:
220 vaccine1.NoDak.edu ESMTP Sendmail 8.13.1/8.13.1; Wed, 26 Oct 2005 16:17:42 -
0500
EHLO nate.cc.ndsu.nodak.edu
250-vaccine1.NoDak.edu Hello nate.cc.ndsu.NoDak.edu [134.129.106.131], pleased 
to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE 26214400
250-DSN
250-AUTH GSSAPI DIGEST-MD5 CRAM-MD5
250-DELIVERBY
250 HELP
MAIL FROM: root@localhost
553 5.5.4 root@localhost... Real domain name required for sender address
MAIL FROM: root
553 5.5.4 root... Real domain name required for sender 
address

Additional info:
In /etc/mail/sendmail.cf, checks are made for various "localhost" addresses. 
"localhost.localdomain" is missing:

# handle case of @localhost on address
R<@> < $* @ localhost > $: < ? $&{client_name} > < $1 @ localhost >

The following line wants adding to this:
R<@> < $* @ localhost.localdomain >     $: < ? $&{client_name} > < $1 @
localhost.localdomain >

Note that localhost.localdomain still remains valid for local use, but not
for remote SMTP use.

-- Additional comment from twoerner on 2006-09-28 05:18 EST --
We used localhost.localdomain since RHEL2.1. So it affects all RHEL releases.