* Dusan wrote:
> 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@ourdomain.sk it will go directly to maiold and when sending to
> johnthomas@ourdomain.sk it will go to the mailnew.

No. Something trying to send mail to you will try
mailold.ourdomain.sk first. If it can talk to it it will talk (E)SMTP
to it, and try and deliver the mail. If mailold.ourdomain.sk rejects
the mail (so for instance if it's for one of the new-style names) it
will bounce. You need to make all the MXs for your domain be able to
accept all mail for it (or, if they refuse it, be correct in so
doing).

--tim