[SOLUTION] Handling Outlook Recurring Meetings: Windowed Expansion + Series Rebuild

[yzhu]

Hi everyone,

I recently struggled with synchronizing recurring Outlook meetings with EspoCRM.
The standard Delta Sync doesn't work well for recurring events.

I documented a complete solution here:

https://www.yzhu.name/2026/01/10/espocrm/08-outlook-recurring-sync-en/

Key points covered:
• Delta Sync for recurring meetings only returns seriesMaster changes
• iCalUId is NOT unique across occurrences (RFC 5545)
• Windowed approach [-7d, +90d] prevents infinite expansion
• Bootstrap state machine for cold-start initialization
• Production checklist (quota limits, DST handling, timezone issues)

Hope this helps others facing the same issue. Feedback welcome!