Category Archives: Postfix

Installing Nagios core on RHEL / CENTOS 5.x – RHEL / CentOS 6.x Fedora 15/16/17/18/19/20

What is Nagios

An enterprise-class monitoring and alerting solution that provides organizations with extended insight of their IT infrastructure before problems affect critical business processes.

Requirements

We require following things for Installing Nagios:
These are Just Pre-requisites. We need them to other things work …

1. Apache and PhP (php is optional)
2. gcc, glib, glibc-common, gd and gd-devel

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Postfix Mail Delivery SMTP Troubleshooting

Articles CentOS Email How To How To's Linux Mail Mail Server Postfix SMTP Tips and Tricks troubleshooting

To avoid delay in emails, specially for gmail. Just find which MX is working by issuing below commands:

# dig mx gmail.com

# telnet mx-IP/name 25

upon success, just see the name of first mx tried from /var/log/maillog

and add an entry in /etc/hosts file.

In my case, the entry is given below:
# vim /etc/hosts

74.125.25.26 aspmx.l.google.com
74.125.25.26 alt1.aspmx.l.google.com
74.125.25.26 alt2.aspmx.l.google.com

:save and exit

now open postfix main.cf and add smtp_host_lookup directive under inet_protocols = all

# vim /etc/postfix/main.cf

inet_protocols = all
smtp_host_lookup=native
save and exit

now restart postfix

# service postfix restart

by default postfix host lookup is done via DNS, native mode uses nsswitch.conf settings and will check /etc/hosts first and then DNS if entry not found in /etc/hosts

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