Yes, I tried it. It did not work.
Here is the problem. My old mailserver has several files in /var/mail. One file for each email account. Each of those files grows as the accounts get new emails and shrink to )KB when the emails are read. There is also one file called 'mail' which is about 6M in size. From reading I divine that is the mbox format. The new server is using Maildir format.
I guess I will need to convert the files in /var/mail to mbox format.