Outlook Missing Appointments 1 - invite or update was deleted

Many of the issues I have to troubleshoot concern appointments missing from someone's calendar.
Before I start re-inventing the wheel, How to troubleshoot missing and duplicate appointments in Outlook already covers some of the background on how appointments go missing. However, by far the vast majority of missing appointment problems I see are caused by one not-so-obvious feature of mail based Calendaring in Outlook:

Deleting a meeting invitation or update will delete the associated appointment*

(*This was changed in Outlook 2007 - I guess someone finally realised how much trouble it causes.)
Today I'll cover some fairly straightforward ways this can trip up the unwary, then post soon with a special case that adds another layer of confusion.
Here's what happens - for versions of Outlook up to 2003, that is:

• Anne invites Bob to a meeting
• Bob accepts the invitation from his Calendar instead of from his Inbox
• This leaves the invite in the Inbox (where accepting from the Inbox would have removed it)
• Bob sees the invite in his Inbox and thinks "I already accepted that, I don't need it" so deletes the invite
• Outlook removes the meeting from the Calendar

The solution to this is for Bob to remember to always Accept or Decline invites from the Inbox.
Another way confusion can occur is in a manager/delegate relationship. Say Claire has a delegate, Dan, who looks after her diary. Dan receives a copy of all Claire's meeting invitations and updates but, critically, so does Claire:

• Dan sees an invitation in the Inbox to a meeting he knows Claire will want to attend, so he Accepts it on her behalf
• Claire also has the invite in her Inbox
• Claire knows Dan has Accepted the invitation on her behalf, so she decides she doesn't need it in her Inbox and deletes it
• Outlook removes the meeting from the Calendar

The solution in this case is to change the Delegate options on Claire's mailbox so that only her delegates receive meeting items. If she really feels that she needs to see them, she'll have to remember not to delete them!
Deleting an Updates to a meeting has much the same effect, like this:

• Evan invites Fiona to a meeting
• Fiona accepts the invitation
• Later, Evan sends out an updated version of the meeting including travel information for out-of-town attendees
• Fiona doesn't need the travel information, so deletes the update from her Inbox
• Outlook removes the meeting from the Calendar

The solution here is for Fiona to make sure she never deletes a meeting update - she should always Accept if she plans to attend or Decline if she doesn't.
A lot of troubleshooting I get involved in, the user is absolutely adamant that nothing they're doing could cause their meetings to disappear, that there must be some gremlin in the system. They've heard it's a problem with BlackBerry/our CRM application/Cached mode/the moon in Taurus/whatever, they've had this problem for months, they're sick of it and they want us to fix it for them. That's when I use my secret weapon - this article from Microsoft:

Outlook meeting requests: Essential do’s and don’ts.

It can take some persuasion to get them to read it (sometimes I say "just so you can give some pointers to the newer team members" or "so you know what to look for when your manager is doing something wrong") but I don't think it's an exaggeration to say 99% of those ongoing problems don't come back when people follow the advice in there.
Next time I'll cover how a meeting organizer can become an attendee and get into an even deeper mess...