When "Choose the mail server" field in Registration Settings policy is a blank, a new user's mail file is created in local disk of Domino Administrator client machine, instead of Domino mail server, even if imported registration text file specifies a user's mail server.
Customer want to keep a blank for "Choose the mail server" field in Registration Settings policy, and they want to specify mail server for each new user in registration text file.
So, the mail server field in Registration Settings policy should be overridden by the value of registration text file.
<Steps>
1. Create explicit policy and Registration Settings policy. "Choose the mail server" field in Registration Settings policy should be a blank as the attached screen shot.
2. Set the explicit policy as default for new user registration. For example, Domino Administrator -> File -> Preference -> Administration Preferences -> Registration -> "Explicit policy" -> Select the above explicit policy.
3. Create registration text file which should specify new user's mail server.
4. Register new user. Use "Import Text File" button and the above registration text file.
5. New user will be registered, but new user's mail file will be created in local disk of Domino Administrator client machine, instead of Domino mail server.
In the admin client, this seems to be a bug for which you should open a support ticket. I'l close this idea anyway because in the new AdminCentral you will be able to create configuration profiles to meet your needs.