Exchange (EWS)

Crate: adapter-ews · Capabilities: calendars, tasks, contacts

Exchange Web Services is the older SOAP/XML API for on-premises Exchange and older Microsoft 365 tenants — used where Graph isn’t available.

Protocol

SOAP over HTTPS. Requests are XML envelopes (soap.rs builds them, mapping.rs parses the responses):

• Autodiscover: the endpoint can be discovered from an email address.
• Sync: SyncFolderItems returns changes for a folder with a sync state token. The adapter first does an id-only probe to learn the change counts cheaply, then fetches item bodies with GetItem.

Authentication

Basic auth (username/password) over TLS, or NTLM depending on the server. The endpoint is discovered or user-supplied.

Quirks

• Folder-complete events. EWS keeps a per-folder in-memory view of every item it has seen, so its event read is folder-complete: it emits the full set with ChangeSet.complete = true, and the host stores an unbounded cache window. This is what fixed a class of “event in a new month doesn’t appear” bugs — the sync cookie is folder-wide, so a range-filtered emit would miss unchanged items in newly-viewed ranges.
• Recurring masters always pass the folder filter; recurrence shapes are enriched via GetItem.
• ChangeKey churn. An edited item keeps its item id but rotates the ChangeKey embedded in the composite id, so the cache purges the whole native group before re-inserting (avoids stale duplicates).

Testing

mockito (or fixture XML) for the SOAP envelopes. Tests cover the id-only folder-sync probe/drain, the count parsing, and the folder-complete emit. Live testing needs an Exchange/365 mailbox that still exposes EWS.