innerjoin

Using Mozilla or Firefox with the calendar extension? or the stand-alone Sunbird?

• Event Identifiers or UIDs
  • Address Harvesting
  • The same event appearing twice in the calendar

The recommended format for 'Unique Identifiers' in RFC2445 is an RFC822 format address spec, see the UID definition on Kanzaki.

However something which looks like an email address will get harvested as if it is an email address and subsequently used for spam.

Is this good or evil?

It depends rather on how your email system is configured. It will certainly increase traffic and if your email system accepts all messages (and delivers to a 'catch all' account), then you'll see an increase in spam. If your system rejects delivery attempts to 'unknown' addresses then you'll be OK.

• Do you get the same event displayed twice in Sunbird/Mozilla Calendar?
• Are you subscribing to a number of different calendars?

Each event has to have its own UID and these should be unique. If Sunbird trusts that the UID is unique it can decide to show the event just the once if it has sees it appearing in a number of calendars.

• An event in one calendar [text/plain]
• The same event in a second calendar [text/plain]

These two calendars contain an event with an identical UID, 1000-innerjoin-org. Sunbird should ideally present this once but it shows the two copies of the same event.