Outlook meeting invites are attachments?

Unanswered Question
Aug 25th, 2008

Just implemented IPs over the weekend and we have some groups we don't want to send un-reviewed attachments. On our older, perhaps crappier email filtering devices, things like meeting requests from outlook would flow through as non-attachments. Responses to them would show up as attachments though.

Is there a quick fix to allow these through (but catching ones that have actual attachments)?

I have this problem too.
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kluu_ironport Mon, 08/25/2008 - 22:24

When I sent a Microsoft Outlook Calendar Invitation to my Gmail address, this is a snippet of what was found in the header of the email that was received:


============================================

------_=_NextPart_001_01C906F7.9431E81B
Content-class: urn:content-classes:calendarmessage
Content-Type: text/calendar;
method=REQUEST;
name="meeting.ics"
Content-Transfer-Encoding: 8bit

BEGIN:VCALENDAR
METHOD:REQUEST
PRODID:Microsoft CDO for Microsoft Exchange
VERSION:2.0
BEGIN:VTIMEZONE
TZID:(GMT-08.00) Pacific Time (US & Canada)/Tijuana

============================================

You may want to test this out but an outgoing content filter that looks for the header field called "Content-Type" with a value of "meeting.ics"

To test this, I would create the outgoing content fiilter this way:

Two conditions:

One condition where it looks for your email address as the sender

Second condition is a header-name("Content-Type") == "meeting.ics"

and then see if it matches correctly. If it matches, then set the action to immediate deliver(). The move this rule to the top.

Donald Nash Wed, 08/27/2008 - 23:48

Yes, invitations are attachments. They have a content type of "text/calendar" (sorry kluu, "meeting.ics" is the file name, not the content type). You can use the "attachment-mimetype" filter rule to detect them, but this rule returns true if any attachment is of this type. A message might have both a "text/calendar" attachment and then something else you don't want to get through. There doesn't seem to be any easy way around this. There is a "drop-attachments-by-mimetype" filter action, but it only lets you list the attachment types to drop. You can't say "drop all attachments except this type".

Incidentally, it is my experience that you shouldn't depend on the "meeting.ics" file name. Our Exchange installation quit putting file names on text/calendar attachments when we upgraded to Exchange 2007. I don't know if this is due to a change in Exchange or a change in our configuration, but in either case "meeting.ics" doesn't appear to be reliable. The "text/calendar" content type is.

buttbutt_ironport Wed, 10/01/2008 - 18:49

thanks. I ended up picking an arbitrary size so most basic invites can go through, larger ones, which may have more data and/or attachments within will still get blocked.

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