Calendar Invitation Email Gone Awry

Here’s some more details on calendar email issue I noted late Monday.

Just after 10pm on Monday, I attempted to migrate my calendar from Google Calendar to Fastmail Calendar1.

I did this by exporting my existing calendar from Google (per https://support.google.com/calendar/answer/37111?hl=en) and then re-importing it back into Fastmail using Apple’s Calendar App. During this re-importing process, it appears that the Fastmail system regenerated the event requests and emailed all the participants of the events; although I initially suspected Apple’s Calendar app.

My wife, who was sitting next to me, was the first to let me know something was awry when she received over 400 emails from me.

After aborting last nights attempt, I tried again to import the data again Tuesday morning by using FastMail’s “Subscribe to a public calendar” feature (https://www.fastmail.fm/help/calendar/publiccalendar.html), which should not have resulted in emails being sent but still did.

In total, 109 people were affected by this issue and up to 2904 emails were sent (1452 from each incident).

Graph of Emails Sent

The good news (if there is such a thing) is that 45% of those affected only received a single email (well, two emails), and 78% of those affected received less than 10 emails (20 emails across both incidents).

Unfortunately, emails were also sent to people even when I was not the original organizer of the event. This accounted for over half the emails that were sent.

I have opened a ticket with Fastmail (Calendar import emailing participants (Ticket Id: 479473)). Fastmail has been prompt and the issue is, in theory, resolved. However, in the future I plan on scrubbing the calendar file of email address to prevent this issue from occurring again.

For those curious, here’s how I extracted2 the number of those affected from the ICS file:

grep -Eiorh 'mailto:([[:alnum:]_.-]+@[[:alnum:]_.-]+?\.[[:alpha:].]{2,6})' "$@" basic.ics | sort | uniq -c | sort -r

Mea Culpa.


  1. there’s a larger story about why, but that’s not important at the moment 

  2. based on mosg’s answer on http://stackoverflow.com/questions/2898463/using-grep-to-find-all-emails/2898907#2898907 

If you got a calendar Invitation from me1, I am so sorry. I’m switching servers, did an export -> import, and Calendar decided to be helpful and email everyone. Face palm.


  1. or maybe a bazzilion invites 

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