How BlueMail keeps your calendar in sync
What actually happens between your device and your provider when an invite arrives, which protocols do the work, and why sync sometimes looks broken when it is not.
Updated
2 min read
Calendar sync is one of those features people only think about when it fails. Then they think about it a great deal, usually in a meeting they are not in.
Here is what BlueMail is doing underneath.
The protocols doing the work
Exchange ActiveSync. The workhorse for Exchange and Microsoft 365. Add the account as ActiveSync and mail, calendar and contacts all sync over one connection, with server-driven push rather than polling. This is why an ActiveSync account feels instant and an IMAP account sometimes does not.
Microsoft Graph. For Microsoft 365 tenants, the modern API surface with token-based access and no password ever stored on the device.
CalDAV. The open standard behind iCloud, Google and most self-hosted calendars. Slower to notify than push protocols but universally supported.
iCalendar files. The .ics attachments that arrive from anyone whose calendar you do not share. BlueMail reads them into your device calendar so a one-off invite from an outside party is a tap, not a transcription job.
What syncs, in both directions
- Events, including recurrence rules and exceptions to them
- Accept, decline and tentative responses, which propagate back to the organizer
- Attendee lists and their responses
- Reminders and alerts
- Time zones, resolved correctly for travel
That last one is the quiet one. An event created in one time zone and viewed in another has to carry the original zone, not a fixed offset, or the whole thing drifts when daylight saving changes. Calendars that store offsets instead of zones are why some meetings move by an hour twice a year.
When it looks broken but is not
The invite arrived as an attachment. The sender’s system sent a plain .ics rather than a calendar invitation. Open it and it lands in your calendar normally.
The event exists but attendees are missing. Some providers only expose the attendee list to the organizer. Nothing is lost, it is simply not shared with you.
A change is not showing. Push tells the device something changed, then the device fetches it. On a metered or heavily restricted connection the second half can be delayed. Pull to refresh forces it.
Everything stopped after a phone update. Check whether the operating system put the app into a restricted battery mode. Aggressive background limits are the single most common cause of “sync stopped working”, and it has nothing to do with the mail client. There is a whole article about that.
Setting it up properly
For Exchange or Microsoft 365, add the account as Exchange rather than IMAP. IMAP carries mail only, so an IMAP-configured work account will never show a calendar no matter how long you wait for it. This one configuration choice accounts for a striking share of support tickets.
For everything else, sign in with the provider’s own login screen and accept the calendar scope when it is offered.
