Can people be warned before an absence starts?

Four days ahead, in two places.

Team Availability shows a scheduled absence as LEAVING SOON and offers an Out of office soon (within 4 days) filter, and a rule's Mention Tag option Add the tag 4 days ahead of the absence tags @-mentions of you from four days before it starts.

Related pages

• Mention Detection and Auto-Reply - where this is covered in full.

• Notifications - more questions on this topic.