Two mail servers on the same domain

[Chris]

"Dusan" <dkulisie at truni.sk> wrote in message
news:bptdna$1062$1 at sf1.isc.org...
> Dear all,
> this is a quite newbie question, I think :)
> We have an old mail server with about 200 users mail accounts.
> We want to exchange it for the new one, and we are planning to use
> following method, which we don't know if it would be correct.
> We want to install a new machine on the same domain and to configure
> mail there (postfix).
> For example a user John Thomas has an account "jthomas" on the old
> mail server. We would make a new account "johnthomas" on the new
> running mail server.
> In the DNS server we would have
> ourdomain.sk  IN  MX 10 mailold.ourdomain.sk.
>               IN  MX 20 mailnew.ourdoamin.sk.
> So our reasoning is that in the case somebody sends an email to
> jthomas at ourdomain.sk it will go directly to maiold and when sending to
> johnthomas at ourdomain.sk it will go to the mailnew.
> By this method we would create all accounts in the new manner...
> Is this correct ?
> And in the case it is not, how this should be done ?
> Thank in advance for your advice
> Regards
> Dusan
>
When sending an email to a domain the only thing that matters as far as DNS
resolution is concerned is the bit after the '@'. So, it doesn't matter if
the mail is for jthomas at ourdomain.sk , johnthomas at ourdomain.sk or
mickeymouse at ourdomain.com. In all cases mail will be delivered to the
primary MX record, in your example mailold.ourdomain.sk.

The best way would simply be to create the same accounts on the new server
and maybe alias some names to the new format if that is what you wish to use
and then simply swap the box out one night for the new one.

Chris.