First we have to add the userparameter in zabbix: vi /etc/zabbix/zabbix_agentd.d/userparameter_postfix.conf and then we have to add into the file following lines: UserParameter=postfix.maildrop, find /var/spool/postfix/maildrop -type f | wc -l UserParameter=postfix.deferred, find /var/spool/postfix/deferred -type f | wc -l UserParameter=postfix.incoming, find /var/spool/postfix/incoming -type f | wc -l UserParameter=postfix.active, find /var/spool/postfix/active -type f | wc -l UserParameter=postfix.queue, mailq | grep -v "Mail queue is empty" | grep -c '^[0-9A-Z]'
Next step is to create in Zabbix the template that these userparameters will be shown .
Now you can enjoy not having issues with your postfix! 🙂