Spammers discovered a better way to get your attention: meeting requests. A meeting request spam will add a tentative appointment to your calendar (or an accepted meeting, if you autoaccept appointments) and pop up a reminder to get your attention.
How do I stop spammers from adding appointments (with reminders!) reminders to my calendar?
When you get a meeting request from a spammer, you need to delete it. If the meeting requests are moved to the junk email folder, they may be added to the calendar as tentative. If you have a default reminder set in Calendar options, a reminder will be set on the "tentative meeting".
See Meetings are not removed when the invitation is deleted for a behavior change in Outlook 2007, Outlook 2010 and Outlook 2013.
Do not decline meeting requests that are spam. Delete both the meeting request and the tentative appointment. In Outlook 2010 and newer, with Conversations enabled, expand the conversation, select both the request and the appointment and delete them.
Use a macro to delete associated appointments
You can use a macro to delete the associated appointment when a meeting request is added to the Deleted Items folder.
See How to use Outlook's VBA Editor if you need help using a macro.
To test the macro without restarting Outlook, click in the Application_Startup macro the click the Run button (or F5).
Private WithEvents Items As Outlook.Items Private Sub Application_Startup() Dim Ns As Outlook.NameSpace Set Ns = Application.GetNamespace("MAPI") Set Items = Ns.GetDefaultFolder(olFolderDeletedItems).Items End Sub Private Sub Items_ItemAdd(ByVal Item As Object) On Error Resume Next Dim Meet As Outlook.MeetingItem Dim Appt As Outlook.AppointmentItem If TypeOf Item Is Outlook.MeetingItem Then Set Meet = Item Set Appt = Meet.GetAssociatedAppointment(True) If Not Appt Is Nothing Then Appt.Delete End If End If End Sub
Create a rule to delete meeting requests
Users who don't received legitimate meeting requests can use a rule to move the requests to the Deleted Items folder, as long as they are in the deleted items folder you won't get the reminders or have it added to the calendar.
Create a rule that "Uses the Form name form" and select Meeting Requests from the Application Forms.
If you receive legitimate meeting requests, you can set exceptions for people in your address book or use subject or words in the body conditions to fine tune the rules.
Remove Reminders from incoming meetings
If you receive legitimate meeting requests with reminders set you can use a VBA macro to remove the reminders from meeting requests. While this will work for meeting spam (and apply equally to valid meeting requests, unless you set exceptions), deleting the messages is better.
Outlook MVP Michael Bauer has this code sample, showing how to delete reminders from incoming meeting requests. Calendar: Delete the reminder of a meeting request.
Change Outlook options for Tentative Appointments
You can configure two Outlook options to reduce the annoyance level of meeting spam.
In Options > Calendar, turn off default reminders. While this will affect appointments you create, you can use an ItemAdd macro to set reminders on appointments marked busy.
If using POP3 or IMAP accounts, you can turn off the 'sniffer'. With the 'sniffer' enabled, the meeting request is automatically added to the calendar as tentative a few minutes after arrival. When it is disabled, a tentative appointment is added to the calendar when you select or open the meeting request.
Turn off the sniffer at File > Options > Mail > Tracking section (Outlook 2010 and up) or Tools > Options > Email options > Tracking, do not select the option to process requests and responses on arrival.
If you are using an Exchange server mailbox, the meetings are added to the calendar as tentative by the Exchange server.