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In Microsoft Outlook, you receive a meeting request from a Lotus Notes user or from another third-party email client. The message contains an attachment that has the following file name:

not supported calendar message.icsAdditionally, when you double-click to open the attachment, you receive the following error:

The file "not supported calendar message .ics" is not a valid Internet Calendar file.


The "not supported calendar message.ics" attachment is created when the original .ics file cannot be converted to an Outlook or Microsoft Exchange meeting type. The conversion fails if one or more of the following conditions are true:

  1. The meeting contains a recurrence pattern that is available to a third-party email client, such as Lotus Notes. However, this recurrence pattern is not supported by Outlook:

    • Monthly by Date: Every month on the nth day and the nth day. Outlook only supports one nth day of the month.

    • Monthly by Day: Every month on the nth day of the week and the nth day of the week. Outlook only supports one nth day of the week in any month.

    • Custom recurrence: Outlook does not support custom recurrence patterns that are available in some third-party email clients, such as Lotus Notes.

  2. The meeting contains a recurrence pattern that is defined by the RDATE property. However, the meeting does not include a corresponding RRULE property. In this case, Outlook does not open the item, even if the RDATE property specifies a supported recurrence pattern


To work around this issue, have the meeting organizer create a meeting that uses a recurring pattern that Outlook supports.

Or, if a Lotus Notes client connects to a Lotus Domino server, the following IBM website provides information about how to manage the recurring meeting options on the Domino server:

Configuring options in Domino 8.5 to improve interoperability with non-Notes calendar users

More Information

When a Lotus Notes recurring meeting is created, and this meeting has a Custom recurrence option, Lotus Notes generates an .ics file that only includes the RDATE property. If you save and open the .ics file attachment that is received in Outlook, you can see that the RDATE property is present. However, you notice that the RRULE property is not present.

Outlook and Exchange depend on the RRULE property to process an .ics attachment and generate the recurring meeting.

For more information about the RDATE and RRULE properties, visit the following page on The Internet Engineering Task Force (IETF) website:
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Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

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