[Dovecot] Disable imap proxy access

[Dominique Feyer]

I work on a dovecot cluster (15 servers) we need to add a new storage
array and move the data for a list of user from the old storage to the
new one. We use dovecot proxy to redirect imap and pop3 to the same
server everytime.

How to disable pop3 and imap access during the data migration process
(duration 5 minutes to 10 minutes). Can i send a custom error message to
our users ?

Thanks for your help

Dominique Feyer