I have finished migrating from 5.5 to 2000 by joining the 5.5 org with a 2000
server etc.

Now when I create a new account with an exchange account, the account is
created and I can logon to the domain with it, but the account has no email
address. By that I mean that the address field is blank.

The default policy shows that an address should be created.

Before I finished the migration, addresses were created in 5.5 then moved to
2000.