[Lula] Mail server ip changed issue.

[Jeff Carlson]

Titu Kim wrote:
>      I wonder how to solve the mail bounce issue
> during the process of switching a mail server from one
> ip to another(same dns name). DNS changes take a while
> for the latest ip to be refreshed. So, before new ip
> information about the mail server is refreshed to
> other dns server, all the mail sent between the gap
> will be bounced. Any idea?

This is actually even easier than Alan suggests (sorry, Alan).

Assuming you have not had any critical problems with DNS in the recent 
past, DNS changes do not take a long time to propagate.  But clients 
will cache responses for the default TTL time.  So what you need to do 
is make these changes at least one TTL time in advance of your MX change.

For instance, if your TTL is one hour, change your DNS one hour ahead of 
time.

First, set your default TTL to about five minutes.  This may cause more 
queries to your DNS server during the migration but it really ought to 
be no problem.

Second, add a secondary MX record that is the new IP of your mail 
server.  So when you make the change, an incoming mailer will first try 
to go to your old IP, fail, then try the new one.

So, it would look like this:

$TTL 300
@                     IN MX 10 old.mail.example.com.
                       IN MX 20 new.mail.example.com.
old.mail.example.com. IN A     10.11.12.13
new.mail.example.com. IN A     172.16.17.18

After you have made the change, reset your TTL and remove the old 
primary MX.
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