Unable to send or receive mails using postfix

1. Check the postfix service if its running or not by executing the command rcpostfix status. The service should be running.
2. Open the file main.cf which should be located at /etc/postfix/ and go to the location where the parameter mydestination is present.
3. Edit the file and add the variable $mydomain and should look like this :- mydestinaion = $myhostname, localhost.$mydomain, $mydomain 
4. Save and exit the file.
5. Open the file master.cf which should be located at /etc/postfix/ and check for the parameter maildrop
6.  Compare the lines which should be mentioned as below:-

maildrop             unix    -       n       n        -         -           pipe

flags=DRhu user=vmail argv=/usr/local/bin/maildrop -d ${recipient}

cyrus                   unix    -      n       n        -         -           pipe

user=cyrus argv=/usr/lib/cyrus/bin/deliver -e -r ${sender} -m ${extension} ${user}

uucp                   unix    -      n       n       -          -           pipe

flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)

ifmail                unix     -      n       n       -         -            pipe

flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)

bsmtp               unix     -      n       n        -        -            pipe

flags=Fq. user=foo argv=/usr/local/sbin/bsmtp -f $sender $nexthop $recipient

procmail         unix      -       n       n       -        -            pipe

flags=R user=nobody argv=/usr/bin/procmail -t -m /etc/procmailrc ${sender} ${recipient}

retry               unix      -       -        n       -        -            error

proxywrite      unix     -       -        n       -       1           proxymap