The mimetype for events is "application/x-vnd.kolab.event". This is the specification of the body contents:
<?xml version="1.0" encoding="UTF-8"?>
<event version="1.0">
<!-- Common fields -->
<uid>(string, no default)</uid>
<body>(string, default empty)</body>
<categories>(string, default empty)</categories>
<creation-date>(datetime, no default)</creation-date>
<last-modification-date>(datetime, no default)</last-modification-date>
<sensitivity>(string, default public)</sensitivity>
{<inline-attachment>(string, no default)</inline-attachment>}
{<link-attachment>(string, no default)</link-attachment>}
<product-id>(string, default empty)</product-id>
<!-- Incidence fields -->
<summary>(string, default empty)</summary>
<location>(string, default empty)</location>
<organizer>
<display-name>(string, default empty)</display-name>
<smtp-address>(string, default empty)</smtp-address>
</organizer>
<start-date>(date or datetime, default not present)</start-date>
<alarm>(number, no default)</alarm>
<recurrence cycle="cycletype" [type="extra type"]>
<interval>(number, default 1)</interval>
{<day>(string, no default)</day>}
<daynumber>(number, no default)</daynumber>
<date>(number, no default)</date>
<month>(string, no default></month>
<range type="rangetype">(date or number or nothing, no default)</range>
{<exclusion>(date, no default)</exclusion>}
</recurrence>
{<attendee>
<display-name>(string, default empty)</display-name>
<smtp-address>(string, default empty)</smtp-address>
<status>(string, default none)</status>
<request-response>(bool, default true)</request-response>
<role>(string, default required)</role>
</attendee>}
<!-- Event specific fields -->
<show-time-as>(string, default busy)</show-time-as>
<color-label>(string, default none)</color-label>
<end-date>(date or datetime, default not present)</end-date>
</event>See Section 4.1> for the description of the common fields
See Section 4.2> for the description of the incidence fields
show-time-as is one of free, tentative, busy, or outofoffice.
color-label can be none, important, business, personal, vacation, must-attend, travel-required, needs-preparation, birthday, anniversary, phone-call. Outlook maps those to colors, hence the name.