SpamFilter will *always*, by default, reject spam emails with an SMTP error code. This SMTP error code will force the sender's mail server to send a bounce email back to the sender. This is extremely important, as the sender will alway be notified of the non-delivery, but this notification will not be sent by your SpamFilter, thus preventing you from sending spam and saving huge amounts of bandwidth.

Going back to your question, in the latest 4.x releases of SpamFilter, if your database is offline, the spam emails to be quarantined will be queued to the \SpamFilter\quarantine directory. When the database comes back online, SpamFilter will automatically insert these pending emails into the quarantine database.