In an AWS EC2 Linux environment, if the log size in /var/log increases rapidly and the log contains "postdrop permission denied" messages, take the following actions. 

Issue 

Dozens of postdrop error messages are written to /var/log/messages and /var/log/maillog every few seconds. 

error: postdrop: warning: mail_queue_enter: create file maildrop/xxxxxx.xxxxx: Permission denied

Due to the increase in error message size, the / filesystem may become full. 

Resolution 

1. Change Permissions 

   # sudo rpm --setugids postfix
   # sudo rpm --setperms postfix

   1. ASIS : rwxr-x-r-x. 1 root postdrop xxxxxx Feb 13 2014 /usr/sbin/postdrop
      TOBE :  rwxr-S-r-x. 1 root postdrop xxxxxx Feb 13 2014 /usr/sbin/postdrop --> Add sticky bit

2. Restart postfix Service 

   # sudo systemctl restart postifx

3. Kill postdrop Process 

   # sudo killall postdrop

4. Clear Error Messages 

   # sudo touch /var/log/messages

5. Restart rsyslog.service 

   # sudo systemctl restart rsyslog.service
   # sudo systemctl status rsyslog.service

    

• Reference : https://access.redhat.com/solutions/1592103