iCalendar is a computer file format which allows Internet users to send meeting requests and tasks to other Internet users, via email, or sharing files with an extension of
.ics. iCalendar is used and supported by a large number of products, including Google Calendar, Apple Calendar (formerly iCal), IBM Lotus Notes, Yahoo! Calendar, Evolution (software), eM Client, Lightning extension for Mozilla Thunderbird and SeaMonkey, and partially by Microsoft Outlook and Novell GroupWise.
VSys One can create and include iCalendar files when it sends e-mails to people based on scheduled events, such as job assignments, trainings and interviews. Whether a letter includes .ics files depends on the letter's content and on if you've checked Include iCalendar/ics files with e-mails in the letter's properties.
Different e-mail programs on the volunteer's end will handle iCalendar files differently (if at all).
Sample iCalendar file
PRODID:-//Bespoke Software///VSys One//EN
ORGANIZER;CN="William A. Cornett":MAILTO:email@example.com
LOCATION:Main bldg. floor 2
SUMMARY:Follow-up - Veronica Bergin
DESCRIPTION:Follow-up - Veronica Bergin\n
123 Main Street\n
Schenectady, NY 12345\n