If a mailbox script or signature tool stopped working this month, check EWS first

Something that wrote to mailboxes stopped working in October? Before you debug the script, check whether it used Exchange Web Services (EWS).

Microsoft's dates, from its own pages:

• From October 2026: EWS is being switched off tenant by tenant. Tenants that never set it get notice in the Message Center, then it's turned off. It can be turned back on for named apps only, through an AppID allow list (EWSAllowedAppIDs).
• 1 April 2027: EWS is permanently blocked, no exceptions, allow list or not.

Older signature tools, mailbox audit scripts and calendar or contact sync jobs are the usual suspects, because EWS was the way to do those things for years.

So, in this order:

1. List everything that touches mailboxes that isn't Outlook itself: scripts, scheduled tasks, third-party tools, anything with a service account.
2. Ask each supplier, in writing, whether it uses EWS and when it moves to Microsoft Graph. "We're working on it" with no date is an answer too.
3. Use the allow list to buy time, not to stand still. It ends on 1 April 2027 whatever you put in it.
4. Signatures are a special case. Graph has no signature endpoint, so a signature tool can't simply swap EWS for Graph. The options left are an Outlook add-in, a mail-flow connector or a transport rule; the guide to central signatures covers what each one can't do.

Checked on 14 October 2026 against Microsoft Learn's EWS deprecation page and the Exchange Team's 3 October 2026 post.