Sendmail and sm-client very slow on boot - Solution

I observer that when database server (Linux 5.x 64-bit) restart "sendmail" and "sm-client" very slow. normally it take 5 to 8 minutes.

currently have a redhat box named "primarydb." /etc/hosts looks like this:

# Do not remove the following line, or various programs
# that require network functionality will fail.
::1 localhost6.localdomain6 localhost6
127.0.0.1 localhost.localdomain localhost
192.168.1.1 primarydb primarydb
192.168.1.2 physicaldb physicaldb
192.168.1.3 logicaldb logicaldb

If I change the hosts file back to it's original setting, this does not occur. Just change /etc/hosts like this, just add one new line:

127.0.0.1 primarydb.localdomain primarydb
or
127.0.0.1 primarydb localhost.localdomain localhost

Contents after changing /etc/hosts, will be like this:

::1 localhost6.localdomain6 localhost6
127.0.0.1 localhost.localdomain localhost
127.0.0.1 primarydb.localdomain primarydb
192.168.1.1 primarydb primarydb
192.168.1.2 physicaldb physicaldb
192.168.1.3 logicaldb logicaldb