An electronic Personal Information Manager (PIM) including a peer-to-peer group scheduling/calendar system is described. The group scheduling/calendar system provides methods for peer-to-peer group scheduling among users, including those users who only have simple e-mail support (i.e., do not have access to the group scheduling/calendar system itself). If a user is able to receive and respond to e-mail, he or she is able to participate in group scheduling in an automated fashion. Under user control, the system generates a scheduling invitation incorporating different formats. Each format includes, in order of increasing content richness, a simple text embedded scheduling invitation, an HTML (Hypertext Markup Language) form embedded scheduling invitation, and a proprietary binary "MIME" (Multipurpose Internet Mail Extensions) scheduling invitation. Each format is designed to transfer the highest degree of information content which a particular target client type can handle. A recipient of the scheduling message employs the messaging format best suited for his or her environment. Regardless of which format the recipient employs, the group scheduling system processes the reply message automatically, with the appropriate information automatically included in the user's group scheduling calendar. The system supports different levels of participation of various individuals throughout various stages of group scheduling, despite the fact that some of the individuals who need to participate might use other proprietary software and reside in other time zones.