Unfortunately Mailbird does not have an 'Out of Office' feature, or an Autoresponder.
We are aware of the fact that an 'Out of Office' feature (also known as an 'AutoResponder') has been requested by a number of customers who would be interested in it, and so we have set up a page where you can vote in favor of introducing this tool. Simply click on the link below to add your vote towards this feature.
While we are sorry that this feature is not currently available, rest assured that every vote counts as part of our development roadmap, so we appreciate the time you will take to vote for this feature.