12. Limit queue processing to root

12. Limit queue processing to `root`
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12. Limit queue processing to `root`

Ordinarily, anyone may process the queue with the -q switch. To limit queue processing to root and the owner of the queue directory, you must specify the restrictqrun option in the /etc/mail/sendmail.cf file.

Edit the sendmail.cf file, vi /etc/mail/sendmail.cf and change the line:

         O PrivacyOptions=authwarnings,goaway,restrictmailq

To read:

         O PrivacyOptions=authwarnings,goaway,restrictmailq,restrictqrun

Now re-start the sendmail process manually for the change to take effect:

         [root@deep] /# /etc/rc.d/init.d/sendmail restart


         Shutting down sendmail:                                    	[  OK  ]
         Starting sendmail:                                    		[  OK  ]

Any non-privileged user who attempts to process the queue will get this message:

         [user@deep /]$ /usr/sbin/sendmail -q


         You do not have permission to process the queue

12.1. The SMTP greeting message

When Sendmail accepts an incoming SMTP connection it sends a greeting message to the other host. This message identifies the local machine and is the first thing it sends to say it is ready.

Edit the sendmail.cf file, vi /etc/mail/sendmail.cf and change the line:

         O SmtpGreetingMessage=$j Sendmail $v/$Z; $b

To read:

         O SmtpGreetingMessage=$j

Now re-start the sendmail process manually for the change to take effect:

         [root@deep] /# /etc/rc.d/init.d/sendmail restart

         Shutting down sendmail:                                    	[  OK  ]
         Starting sendmail:                                    		[  OK  ]

This change doesn't actually affect anything, but was recommended by folks in the news.admin.net-abuse.email newsgroup as a legal precaution. It modifies the banner, which Sendmail displays upon receiving a connection.

Do set the immutable bit on important Sendmail files, important Sendmail files can be set immutable for better security with the chattr command of Linux. A file with the +i attribute cannot be modified, deleted or renamed. No link can be created to this file, and no data can be written to the file. Only the super-user can set or clear this attribute.

Set the immutable bit on the sendmail.cf file:

         [root@deep] /# chattr  +i /etc/mail/sendmail.cf

Set the immutable bit on the local-host-names file:

         [root@deep] /# chattr  +i /etc/mail/local-host-names

Set the immutable bit on the aliases file:

         [root@deep] /# chattr  +i /etc/mail/aliases

Set the immutable bit on the access file:

         [root@deep] /# chattr  +i /etc/mail/access

Further documentation and for more details, there are several man pages you can read:

aliases(5): - aliases file for sendmail
makemap(8): - create database maps for sendmail
sendmail(8): - an electronic mail transport agent
mailq(1): - print the mail queue
newaliases(1): - rebuild the data base for the mail aliases file
mailstats(8): - display mail statistics
praliases(8): - display system mail aliases

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11. The `/etc/mail/aliases` file	Home	13. Sendmail Administrative Tools