Can a Google Workspace calendar export be too messy to import into Fastmail cleanly?

Yes. Large historical exports with recurring events, alarms, and legacy metadata often need repair before import behaves predictably.

What made this migration unusually hard?

The file had roughly 30 years of history, more than 12,000 events, thousands of alarms, and signs of multiple prior migrations across calendar ecosystems.

What should I do if my Google Workspace to Fastmail migration is breaking?

Try the normal import flow first for a small clean export. If the file is large, old, or already showing duplicate, timezone, or recurrence issues, validate and repair it before importing again.

How We Repaired a 30-Year Google Workspace Calendar for Migration to Fastmail

Most calendar migrations are supposed to be boring: export the old calendar, import it into the new one, and move on.

This one was not.

A user moving from Google Workspace to Fastmail had a calendar with roughly 30 years of history. The export looked like a normal .ics file at first, but it carried the kind of baggage that builds up when a calendar has lived through multiple systems over many years.

The result was not just a routine import job. It was a calendar repair problem.

If you are making the same move and your import is breaking, start with the practical guide: Google Workspace to Fastmail calendar migration.

If you already have a broken file, go straight to /fix.

1. Why this calendar was unusually hard

This export was not a small, recent team calendar. It looked more like a long-lived personal or work calendar that had accumulated years of changes, recurring events, alarms, and legacy metadata.

The file was roughly:

6.4 MB
231,961 lines
12,438 events
2,552 alarms

It also showed signs that the calendar had likely moved between ecosystems before. That matters because old imports, legacy fields, and mixed metadata often make later migrations harder.

For a calendar like this, “just import the file” stops being serious advice.

2. What tends to break in migrations like this

When a large historical calendar moves from one provider to another, the visible failure is often simple, but the root cause is not.

Common symptoms include:

Duplicate events after import
Recurring events behaving differently in the destination calendar
Timezone drift or historical events appearing at the wrong hour
Import failures with vague or unhelpful error messages
A file that is technically an ICS export, but too large or messy to trust without cleanup

If that sounds familiar, these guides may help:

3. Why normal cleanup advice stops helping

For a small export with a few recent events, manual cleanup can be enough.

You can often:

re-export the calendar
import into a test calendar first
remove obvious duplicate calendars
check a few recurring events and timezones

But once a file gets large enough, old enough, or messy enough, the problem is no longer one bad event.

It becomes the interaction of:

scale
recurrence rules
legacy alarms
mixed metadata from different calendar systems
years of imported history

At that point, asking someone to hand-edit raw ICS text is usually unrealistic.

4. The repair path this migration needed

Supporting this migration led directly to the repair workflow CorrectICS now uses for very large or very messy calendar files.

The important point is not the internal implementation. The useful takeaway is simpler:

Some migration files are too large or too complex for a normal, quick cleanup flow, but they can still be repaired.

That matters for users moving to Fastmail because the migration job is time-sensitive. You do not want to wonder whether years of calendar history imported cleanly, duplicated silently, or shifted across timezones.

If your export is unusually large, already failing, or clearly carrying legacy baggage, validate it before repeated imports make the situation worse.

5. What to do if you are migrating from Google Workspace to Fastmail

A practical approach:

Export from Google Workspace using the cleanest source calendar you can.
Import once into a test calendar in Fastmail if possible.
Check a few important areas first:
- recurring meetings
- older historical events
- timezone-sensitive appointments
- reminders/alarms
If you see duplicate events, wrong times, or a failed import, stop repeated retries.
Run the file through CorrectICS to validate and repair the export before importing again.

For the step-by-step migration workflow, use: Google Workspace to Fastmail calendar migration.

6. When CorrectICS is the right fit

CorrectICS is most useful here when:

the export is large or long-lived
the calendar has clearly been through multiple migrations already
Fastmail import behavior is producing duplicates, recurrence oddities, or timezone issues
the file is too messy for realistic manual cleanup

For very large or complex migration files, CorrectICS can route you to the right repair path instead of leaving you stuck with trial-and-error imports.

7. The takeaway

The lesson from this Google Workspace to Fastmail migration was not that every provider switch is dangerous.

It was that some calendar exports are really historical data artifacts, not clean handoff files.

If your migration is already showing signs of trouble, treat it like a repair job early. That is faster, safer, and much less frustrating than trying the same broken import over and over.

Next steps:

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