Sendmail (unresolved host name)

[_m3]

.test
.example
.invalid
.localhost

".test" is recommended for use in testing of current or new DNS
related code.

".example" is recommended for use in documentation or as examples.

".invalid" is intended for use in online construction of domain
names that are sure to be invalid and which it is obvious at a
glance are invalid.

The ".localhost" TLD has traditionally been statically defined in
host DNS implementations as having an A record pointing to the
loop back IP address and is reserved for such use. Any other use
would conflict with widely deployed code which assumes this use.
...
The Internet Assigned Numbers Authority (IANA) also currently has the
following second level domain names reserved which can be used as
examples.
example.com
example.net
example.org

http://www.rfc-editor.org/rfc/rfc2606.txt

=> meinserver.example.com

HTH