Outlook Calendar and Twilio integrate through Microsoft Power Automate and the Microsoft Graph API combined with the Twilio Messages API to send SMS reminders to external meeting attendees before scheduled events, addressing the common failure mode where email calendar notifications are missed or buried. This integration is built for organizations running Microsoft 365 who need to send SMS reminders to clients, prospects, or external partners invited to Outlook meetings without those attendees needing to install or configure anything on their end. Power Automate provides the trigger and scheduling logic connecting Outlook Calendar event data to the Twilio connector, with Microsoft Graph providing attendee details and phone lookups.
What You Need Before You Start
Ensure your Microsoft 365 account has Power Automate access at the Per User or Per Flow plan, as the free plan does not support the premium Twilio connector or the Microsoft Graph API connector required for this integration. Create a Twilio connection in Power Automate by searching for the Twilio connector, clicking Sign in, and entering your Twilio Account SID and Auth Token to authorize Power Automate to call the Twilio Messages API on your behalf. Store attendee phone numbers in Azure Active Directory user profiles under the Mobile Phone field in the user's contact information, as Power Automate can query AAD via the Microsoft Graph connector to retrieve phone numbers for invited attendees who are members of your tenant. From Twilio, collect your Account SID, Auth Token, and an SMS-capable phone number registered for A2P 10DLC, and note that external attendees not in your AAD tenant will require a secondary lookup from a SharePoint list or Excel table mapping their email to their mobile phone.
Step-by-Step Integration Guide
Create a Power Automate scheduled flow set to run every hour using the Recurrence trigger with an interval of 1 and frequency of Hour, then add the Office 365 Outlook Get Events action targeting your calendar with a time range of now to now plus 2 hours using the utcNow() expression for the start and addHours(utcNow(), 2) expression for the end, filtering to events that start in the next 60 to 120 minutes. Add an Apply to Each control over the events returned, and within it add a Get Attendees action or use the event body's Attendees array, then for each attendee add a Get User action from the Azure AD connector using the attendee email to retrieve the AAD profile and read the MobilePhone field from the user object. Add a Condition action that checks whether the MobilePhone value is not empty, then in the Yes branch add the Twilio Send Text Message action with the To field set to the MobilePhone value, the From field set to your Twilio number, and the Body field set to a dynamic string composed from the event Subject, Start time formatted using the formatDateTime function, and the event join URL extracted from the OnlineMeeting.JoinUrl field of the event object. Add tracking to prevent duplicate SMS by storing each processed combination of event ID and attendee email in a SharePoint list using the SharePoint Create Item action, and add a SharePoint Get Items filter at the beginning of the loop to check whether a reminder has already been sent for that combination before dispatching Twilio SMS.
Common Issues and How to Fix Them
Power Automate's Get User action fails for external meeting attendees who are not members of your Azure Active Directory tenant, returning a 404 Not Found response that causes the flow to error on the error handling branch. Add a Scope action around the Get User call with an error handler that catches the 404, then look up the attendee phone from a SharePoint fallback list using a SharePoint Get Items action filtering on the attendee email, enabling phone lookup for both internal AAD users and external attendees stored in the SharePoint list. The Outlook Calendar Get Events action does not return attendees for all-day events or events created outside of Outlook such as imported ICS files, causing those event types to have an empty attendees array. Add a Condition before the Apply to Each loop that checks whether the event IsAllDay field is false and the attendees array is not empty, routing all-day events and attendee-less events to a different path that skips SMS dispatch. Power Automate scheduled flows sometimes skip a run silently when the Microsoft cloud infrastructure experiences a brief scheduling delay, and the window for catching 60-minute pre-meeting events becomes 0 minutes wide. Expand the reminder window to events starting in 45 to 90 minutes rather than exactly 60 minutes by using the addMinutes(utcNow(), 45) and addMinutes(utcNow(), 90) expressions for the filter range, giving the flow a wider catch window that tolerates minor scheduling delays.
How to Get More from This Integration
Build a new meeting notification flow triggered on the Office 365 Outlook When an event is added trigger, which fires when a new calendar event is created, and dispatch a Twilio SMS to all attendees immediately after creation so they receive an SMS in addition to the standard email invitation, achieving higher immediate awareness especially for urgent meetings. Add a meeting cancellation SMS by creating a second Power Automate flow triggered on the Office 365 Outlook When an event is modified trigger, checking whether the event IsCancelled field changed to true, and dispatching a Twilio SMS to all attendees notifying them that the meeting has been cancelled and optionally suggesting a rescheduling action. Create a Teams meeting start alert by using the Microsoft Graph connector to retrieve the Teams meeting join URL from the event's onlineMeeting.joinUrl property and including it in the 15-minute Twilio reminder SMS so attendees can join directly from the text message without searching their email. Extend the integration to external clients without AAD accounts by building a SharePoint-based phone registry where your team adds the client email and mobile phone when booking an external meeting, and the Power Automate flow queries that SharePoint list for the phone lookup before dispatching each Twilio reminder SMS.
Conclusion
Outlook Calendar and Twilio together ensure every meeting attendee receives a timely SMS reminder through the Microsoft 365 platform your organization already runs, reducing no-shows without requiring any additional tools outside your existing stack. Contact Telphi Consulting to design and build this Power Automate Twilio reminder flow for your organization.
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