Qmail is one of the favorite MTA’s of server admins and needless to mention most of us use qmailrocks documentation qmailrocks.org for installing it.

Even after following the complete steps you still will have problem with the mail service, like when you try to test the connectivity to mailserver using telnet you will get the error like

 Connection closed by foreign host

immediately.

Next thing you need to do is to tail the log file of smtpd

 tail /var/log/qmail/qmail-smtpd/current 

You will see the output something like

 /var/qmail/bin/qmail-smtpd: error while loading shared libraries: libselinux.so.1: failed to map segment from shared object: Cannot allocate memory 

The problem is with the softlimit set in

 /var/qmail/supervise/qmail-smtpd/run  

go the the line

 exec /usr/local/bin/softlimit -m 30000000   

and change it to

 exec /usr/local/bin/softlimit -m 50000000  

restart qmail

qmailctl stop
qmailctl start 

Your mailserver still have problems in sending mails, you should also check whether the RDNS set for the main ip of the server

Good to go

admin linux, Mailservice qmailrocks softlimit