Replying to emails from M365 Outlook group
A problem I am stumped with, so I am reaching out for some help/guidance. One group wants to not have the emails going into their own inbox but manage and reply only from the group inbox itself (so they know the email has been processed by deleting it once replied). It worked OK to begin with and then some users couldn't reply, then more. Some still can. I have tried reindexing local copy, using browser instead of app & changing the send on behalf of permissions. Owner or member of group doesn't seem to make a difference. Error messages include "This message can't be sent because it no longer exists. It can only be discarded. Make sure you copy the contents of the message before you discard if you want to use them later." and "Couldn't send this message". Please see screenshots attached. My questions: 1: Is Outlook on M365 designed to allow users to reply from the group either as the "group" or as themselves? Information I found isn't clear. 2: If it is / can be - what can I do to make it work for all users? Thanks!How to Check if Shared Mailboxes Need MDO Licenses
Shared mailboxes might need Microsoft Defender for Office 365 licenses, but how do you identify how many licenses? We use PowerShell to do the job by analyzing external email sent to shared mailboxes. If a mailbox receives external email, then by definition the mailbox receives benefit from MDO, and that’s the test for requiring a license. https://office365itpros.com/2025/11/25/microsoft-defender-for-office-365-3/Microsoft Launches Preview of Exchange Admin API
Microsoft launched the preview of the Exchange Admin API on November 17. The new API is intended to close known feature gaps that exist in the Graph APIs and allow developers to migrate from EWS before Microsoft retires EWS in October 2026. Think of the Exchange Admin API as a discardable time-limited API that allows clients to submit cmdlets for processing. It’s certainly one way to approach the EWS problem! https://office365itpros.com/2025/11/18/exchange-admin-api-preview/
Outlook Encrypted Email Issues
I have deployed M365DLP controls to block password protected atachments that cannot be scanned and am telling users to use Outlook Encryption instead to protect outgoing email attachments. However, a number of external companies have reported not being able to open the encrypted messages and the screenshots provided show that they are trying to authenticate as a guest user in my Entra ID instance (rather than using their own IdP, SSO or an OTP). What would cause that and how do I resolve?
Title: Expose SHA-256 or SHA-1 for Mail Attachments in Microsoft Graph
Problem Email attachments in Graph don’t include a content hash. To identify or match attachments, developers have to download the entire file first. That wastes bandwidth and time and increases exposure. OneDrive/SharePoint already return hashes, but mail does not, so experiences are inconsistent. Request Add a server-provided content hash to every mail attachment. Prefer SHA-256. If that’s not feasible initially, expose SHA-1 as a minimum to align with existing Drive item hashes. Benefits Faster and cheaper: avoid downloading large files just to tell if you already have them. Deduplication: detect repeated attachments across threads and mailboxes. Security operations: correlate attachments with threat intel by hash and triage suspicious emails without fetching payloads. eDiscovery and compliance: confidently match the same document across mail and files. Consistency: a predictable, uniform approach across Mail and OneDrive/SharePoint.
Unified Company Calendar for Mixed Microsoft 365 and Non-365 Users – 2025
Seeking a Shared Calendar Solution for Mixed Microsoft 365 and Non-365 Users I’m working on a solution to create a shared company calendar that everyone in our organization can view, while keeping editing permissions limited to a few selected individuals. The challenge: Some of our team members do not use Microsoft 365, and I’d like them to still be able to subscribe to or view the calendar and receive updates. Ideally, this should work without requiring full Microsoft accounts. I initially considered using an ICS-based calendar, but it seems Microsoft 365 Group calendars don’t support sharing via ICS links. I also explored creating a Group calendar as suggested in other threads, but ran into issues making it accessible to external users or those without 365 accounts. For context, I’m a Global Admin, so I have full access to configure settings in the Microsoft 365 Admin Center and Exchange if needed. We’re a small business, and our main goal is to have a centralized calendar for vacation schedules and company-wide events. It should be simple to access and maintain, with a focus on collaboration and accessibility across the board. What I’m looking for: A calendar that’s viewable by all, including non-M365 users Editable only by a few delegated team members Compatible with Microsoft 365, but not dependent on it for basic access Any tools, workarounds, or best practices that have worked for others in similar hybrid environmentsExchange Online Basics – How Email Works in Microsoft 365
In today’s business environment, email remains a critical communication tool—and increasingly, it’s running entirely in the cloud. If your organization uses or is considering using Exchange Online as part of Microsoft 365 (or even standalone), it’s helpful to understand how email works in that context: what happens behind the scenes, what you need to set up, and how to ensure things run smoothly and securely. This article guides you through the basics of Exchange Online mail flow, architecture, administration, and security. https://dellenny.com/exchange-online-basics-how-email-works-in-microsoft-365/Microsoft Issues Updated Guidance for Defender for Office 365 Licensing
Some inconsistencies in the MDO P2 service description and licensing terms exposed a need for tenants to license every user and shared mailboxes. Microsoft has changed the service description and licensing terms to make them simpler. Mailboxes still need MDO licenses, but only if they benefit from MDO protection, including MDO P2 if that’s what they use. Tenant admins have some extra work to do to deploy policies. All explained here. https://office365itpros.com/2025/10/31/mdo-p2-licensing/
