text/calendar

iCalendar's wire format — the .ics file behind every meeting invite. The method parameter is what turns a bare calendar file into a scheduling message: without method=REQUEST in the type, Outlook shows an attachment instead of accept and decline buttons, making this the most-debugged parameter in calendar email. RFC 5545 defines the format; the invite choreography lives in iTIP and iMIP on top of it. UTF-8 throughout.

.ifb is the rarely seen free/busy-only variant.

Defined by RFC 5545 · IANA registration. Registry facts from the IANA media-types registry via mime-db.