[Exim] hold_domains = *

Quick question:

Tomorrow we are migrating our entire mail store to a new filer. This will mean
switching off POP/IMAP access to the mail store for around 1 hour. However, we
wanted to force all mail to be queued during the migration to avoid bouncing
mail... From what I read all we need to do is add the following line to our
exim config...

hold_domains = *

..and of course restart exim. Will this be enough to ensure that there will be
no 'writes' to our mail store? I just wanted to check there were no gotchas or
things to be aware of!

Cheers,
Ray