I have a server running postfix and dovecot with a local mysql database to store virtual domains and users. I'm considering to move the database to another server and perhaps switch to using ldap instead of mysql to store the users and virtual domains.
What is the behaviour of postfix when it can't reach the database to lookup a recipient? If the server hosting the database would go down for some time, would postfix start dropping incoming mail because it can't lookup the recipents or would it queue the mail until the database is reachable again and at that time check if the destination is a valid recipient.
If it queues the mail, how long is it possible to queue it and any difference between mysql and ldap in this regard?