What happens if email is delayed by the filter?
Delays of 10-15 minutes are very common shortly after setting up the spam-filter for the domain.
This is a result of the self learning system of the filter: it does not know the receiving mail server yet, and will grey-list the e-mail first. The next delivery attempt of the sending mail server (after a minimum of 10 minutes), the filter will accept the e-mail and process with the next validation steps.
After receiving 5 to 10 e-mails, the recipient mail-server will be recognised and the delay will disappears.