22.12. 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
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O PrivacyOptions=authwarnings,goaway,restrictmailq,restrictqrun
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Now re-start the sendmail process manually for the change to take effect:
[root@deep] /# /etc/rc.d/init.d/sendmail restart
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Shutting down sendmail: [ OK ]
Starting sendmail: [ OK ]
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[user@deep /]$ /usr/sbin/sendmail -q
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You do not have permission to process the queue
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22.12.1. 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; $b
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O SmtpGreetingMessage=$j
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[root@deep] /# /etc/rc.d/init.d/sendmail restart
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Shutting down sendmail: [ OK ]
Starting sendmail: [ OK ]
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: 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.cfSet the immutable bit on the local-host-names file:
[root@deep] /# chattr +i /etc/mail/local-host-namesSet the immutable bit on the aliases file:
[root@deep] /# chattr +i /etc/mail/aliasesSet 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