You could
change your /etc/resolv.conf file to use the new name servers, but that isn??™t advisable
until you are certain the new name servers are working correctly. Instead, simply
cause dig(1) itself to use the new name servers:
% dig @nameserver host
Here, the @ is immediately followed by the hostname or IP address of the name server
to use instead of the default. The dig(1) program will perform its lookups directly
using the name servers specified. Consider:
% dig +short mx your.domain
0 mail.your.domain
10 mail2.your.domain
% dig +short @123.45.67.89 your.domain
1 mailserver.new.isp
10 mail.your.domain
Here, we first look up the local domain using the current name servers (there is no @
argument) and find that the output from dig(1) is correct. We then look up the local
domain at the new name server using its IP address (the @123.45.67.89) and discover
that they are set up incorrectly. This discovery gives you time to fix your MX records
on the new name servers before you actually switch services to them.
9.5 Pitfalls
??? When sendmail finds multiple A or AAAA records for a host (and no MX
records), it tries them in the order returned by DNS, but looks up and uses
AAAA before A records. If sortlist is specified in the /etc/resolv.conf file, DNS
returns the A or AAAA record that is on the same network first. The sendmail
program assumes that DNS returns addresses in a useful order.
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