Mail server not working when configured with IP address

[vz7r1x]

Hi All!
Sendmail works with host name but fails when I replace hostname with IP address in sendmail.cf
DSXXX.XXX.30.30

mail log output:
Apr 28 08:19:39 rookie sendmail[26344]: p3SCJcoB026342: p3SCJdoA026344: DSN: Host unknown (Name server: XXX.XXX.30.30: host not found)
-------
more /etc/nsswitch.conf
# /etc/nsswitch.conf:
#

hosts: files [NOTFOUND=continue] dns
passwd: files
group: files
services: files
networks: files
protocols: files
rpc: files
publickey: files
netgroup: files
automount: files
aliases: files
-------
more /etc/resolv.conf
domain ABC.CDE.FGH.mil
nameserver XXX.XXX.20.11
nameserver XXX.XXX.20.12

/etc/hosts also has the entry for mail server.
XXX.XXX.30.30 mailServer.com mailServer

My mail server name changes frequently so we are asked to use IP.

Can you help?
Thanks

[Bill Hassell]

Take a look at /etc/mail to see if you have a service.switch file. This file can specify how to resolve a hostname and IP and overrides resolv.conf.

[Matti_Kurkela · Accepted solution]

If you're going to use an IP address in the smarthost definition in sendmail.cf, put [square brackets] around the address.

i.e.

DS[XXX.XXX.30.30]

MK

[vz7r1x]

Thanks, sendmail is working great with your suggestion.

[vz7r1x]

Thx