Migrate system users to virtual users

[Ron Leach]

List, good afternoon,

We are at the planning stage of wanting to migrate from an existing 
installation onto a new machine, and also to change from system users 
to virtual users.  May I check that our ideas for user id are correct?

I am not sure whether we will encounter a 'permissions' and 'user id' 
problem when moving from a system-user scheme to a virtual scheme.  We 
use Maildir, and the maildirs at the moment are in their users' linux 
/home directories.

After reading the wiki, we think that the 'single system user for 
vmail' arrangement, ie just one system user to manage all the mail for 
all virtual users, will work for us.  I think that means that the 
permissions on all our existing 'system-user-oriented' maildirs will 
have to be changed (in the new machine) so that they are owned by the 
'single-system-user', such as 'vmail'.

One thought was to first copy the existing maildirs into the new 
virtual user file system tree, and then, second, change the owners and 
permissions on the maildirs and directories and messages to permit 
control by 'vmail'.  From the point of view of transferring all the 
mail files, is that all we would have to do?  (Of course, we would 
also have to create the virtual users and their passwords, and arrange 
the appropriate password lookups etc, but that's not the direct topic 
of this post.  And that arrangement has to be compatible with the MTA, 
as well.)

If we do copy the maildirs and change the permissions, does all the 
metadata that the clients, or Dovecot, use to detect new, existing, or 
downloaded mail remain valid?  Or should we use a different approach?

Grateful for any comment

regards, Ron