From phpBB Development Wiki
Bots are phpBB users which are used for web crawlers (such as Google Search) in order to list them with their name in the "who is online" section and more. However the users are treated in other ways.
Receiving Private Messages
Bots do not receive PMs.
Bots cannot receive PMs. However code dealing with PMs should not need to know about bots, it should simply use the regular option for whether a user can receive PMs.
Receiving Mass E-Mail
Receiving E-Mail/XMPP Notifications (Posts/PM)
Bot user profiles are displayed like regular users for users with a_user permission and founders