Exchange SE HU6: PDF attachments truncated to 13 KB via Outlook Desktop — OWA unaffected
We've spent days isolating this and ruled out everything we could touch. The corruption survives agent disabling, Bitdefender removal, and BypassFiltering — and the message tracking logs show exactly where it happens. Environment: Exchange Server SE, Build 15.2.2562.41 (HU6 / KB5081755), Windows Server 2025 Problem: PDF attachments sent internally via Outlook Desktop (MAPI) arrive corrupted at ~13 KB (original: ~32 KB, no xref/EOF). All PDF sizes, all internal recipients affected. Started 21 May 2026. Key finding — OWA works, Outlook Desktop doesn't: Sending the identical email via OWA → attachment arrives intact. Outlook Desktop → truncated. Message tracking proof: Both paths deliver the message at full size (~42 KB) via STOREDRIVER DELIVER. Only the Outlook Desktop delivery shows an additional X-SDDS=0.106 step in the STOREDRIVER latency breakdown. That step does not appear in the OWA delivery. The corruption happens inside that MAPI/TNEF store write step — not in transport. Systematically ruled out: All transport agents disabled → still 13 KB Exchange Malware Agent + Set-MalwareFilteringServer -BypassFiltering $true → still 13 KB Bitdefender GravityZone fully uninstalled from server → still 13 KB EEMS mitigations: only PING1 and M2.1.0 applied, neither affects MAPI delivery Temporal correlation: Three Windows updates installed 21.05.2026: KB5087051 (.NET Framework 4.8.1), KB5087539 (Windows Server 2025 CU), KB5089717 (Servicing Stack). Exchange SE HU6 (KB5081755) was installed around the same period. Workaround: Sending via OWA works. Not acceptable long-term. Has anyone seen this? Is this a known regression in HU6 or KB5087051?
FIX - Outlook 2013,2016,2019 fails open mailbox Exchange 2019 on-prem in offline LAN
Exchange 2019 on-prem + Outlook 2013/2016/2019 in offline LAN Symptoms: - OWA works - ECP works - Autodiscover works - Test-MAPIConnectivity is successful - Outlook profile can be created - Outlook fails to open the mailbox / “Cannot start Microsoft Outlook” / “The set of folders cannot be opened” / “The attempt to log on to Microsoft Exchange has failed” - Environment has no internet connection Root cause: The Windows client had a default gateway configured, but the gateway IP did not respond to ping. In our case the client received 192.168.1.1 as default gateway, but this IP was unreachable in the offline network. Fix: Set the client default gateway to an existing reachable IP address, for example the Exchange/DC server IP 192.168.1.5. Internet access is not required, but the default gateway must be reachable/responding. After changing: Default gateway: 192.168.1.5 DNS: 192.168.1.5 mail/autodiscover DNS or hosts pointing to Exchange 2019 Result: Outlook 2013, Outlook 2016 and Outlook 2019 connected to Exchange 2019 successfully.HVE for Microsoft 365: When to Use It, When Not To, and Who Should Be Allowed to Send at Scale
Microsoft recently announced the General Availability of High Volume Email for Microsoft 365, also known as HVE, in Exchange Online. This is an important and long-awaited capability for organizations that need to send large volumes of internal email from applications, devices, or line-of-business systems without using regular user mailboxes as bulk-sending engines. But HVE should not be misunderstood. It does not mean that every mailbox in Exchange Online should now be used for mass email. It does not mean Exchange Online has become a general-purpose marketing platform. And it does not remove the need for proper outbound email governance. Why HVE Matters For years, many organizations have used regular Exchange Online mailboxes, shared mailboxes, or service accounts to send automated messages from applications, scanners, monitoring platforms, ticketing platforms, and custom business applications. That approach creates several problems. Standard mailboxes are designed for human and business communication, not for sustained high-volume automated traffic. Exchange Online has recipient limits, message rate limits, outbound spam protections, and tenant-level controls to protect the service and reduce abuse. HVE introduces a more appropriate model for specific high-volume scenarios. Instead of using a normal mailbox for automated traffic, organizations can create dedicated HVE accounts and use specific SMTP endpoints, admin controls, reporting, and governance for approved high-volume internal messaging scenarios. What HVE Is Designed For HVE is designed for automated, operational, and transactional messaging at scale, primarily for internal recipients within the tenant. Examples include: Internal application notifications. Line-of-business system messages. Device-generated messages. Operational alerts. Security advisories. Internal workflow communications. Monitoring platform alerts. IT service notifications. Large-scale internal announcements generated by systems. This is especially relevant when the organization needs to send messages at scale but still wants to keep the workload within Microsoft 365 governance and Exchange Online mail flow. In practical terms, HVE is useful when the sender is not a human user, but a controlled business system. What HVE Is Not HVE is not a replacement for marketing platforms. HVE is not a general-purpose internet bulk email engine. HVE is not a way to bypass Exchange Online sending limits for external campaigns. HVE is not the correct platform for newsletters, promotional campaigns, large-scale customer communication, or high-volume external transactional email. For external transactional, marketing, or customer-facing bulk email, organizations should evaluate platforms designed for that purpose, such as Azure Communication Services Email, SendGrid, Amazon SES, Mailchimp, Brevo, or another specialized delivery platform. When to Use HVE Use HVE when the workload matches these characteristics: The sender is an application, device, service, or business system. The recipients are primarily internal users in the Microsoft 365 tenant. The volume is higher than what should be sent from a standard mailbox. The workload is operational, automated, or transactional. The organization needs centralized Microsoft 365 administration and reporting. The organization wants to avoid impacting user mailbox sending limits. The use case is approved, documented, monitored, and governed. Good examples: A security platform sending internal security advisories. A monitoring system sending infrastructure alerts to internal teams. A business workflow system sending high-volume approval or status notifications. An IT service platform sending internal notifications. A service management platform sending ticket updates to internal users. A device management system sending operational messages to internal teams. When Not to Use HVE Do not use HVE when the workload is external bulk email. Avoid HVE for: Marketing campaigns. Newsletters to customers. Promotional email. Mass external invitations. External transactional email at scale. Customer invoices and receipts in high volume. OTP or password reset flows for external users. External portal notifications. Any workload where deliverability, bounce handling, reputation management, unsubscribe handling, analytics, or customer consent management are required. Those workloads require a platform designed for external delivery, reputation management, suppression lists, opt-out, tracking, bounce handling, and compliance. Who Should Be Allowed to Use HVE HVE should not be enabled casually for every team or every application. It should be treated as a controlled platform capability. Recommended eligible senders: Approved line-of-business applications. Corporate systems owned by IT, Security, Operations, Facilities, or Service Management teams. Managed devices or services with a clear business purpose. Internal platforms that send operational messages to employees. Applications with documented ownership, authentication, monitoring, and expected volume. Recommended non-eligible senders: Normal users. Shared mailboxes used by humans. Marketing teams sending to external audiences. Unmanaged scripts. Legacy systems with no owner. Applications with unknown volume. Systems that send to external recipients at scale. Any application using HVE just to avoid standard mailbox limits. The core principle is simple: HVE should be enabled for workloads, not for convenience. Governance Model Before enabling HVE, organizations should define a governance model. At minimum, each HVE account should have: A named business owner. A technical owner. A documented purpose. Expected daily and monthly volume. Recipient scope. Authentication method. Monitoring process. Incident response path. Decommissioning criteria. Review frequency. HVE accounts should not become invisible service accounts that nobody owns. They should be treated as privileged communication identities. Security and Authentication HVE supports OAuth authentication, and Microsoft provides guidance for restricting OAuth authentication to specific Microsoft Entra ID applications. This is important because organizations should avoid broad, uncontrolled access. They should restrict which applications can send through each HVE account, monitor usage, and separate workloads by purpose. For example: One HVE account for security alerts. One HVE account for monitoring systems. One HVE account for IT service notifications. One HVE account for internal operational communications. This separation improves visibility, investigation, accountability, and risk containment. HVE vs Standard Exchange Online Mailboxes A standard Exchange Online mailbox should be used for normal human communication. A shared mailbox should be used for collaborative business processes. An HVE account should be used for approved high-volume internal system email. A dedicated external delivery platform should be used for marketing, bulk external communication, or high-volume transactional email. Scenario Recommended Platform Human business email Exchange Online mailbox Team or department mailbox Shared mailbox Low-volume application notifications Standard Exchange Online, if approved High-volume internal system notifications HVE Internal operational alerts at scale HVE Marketing campaigns Marketing platform External transactional email Transactional email service Customer newsletters Marketing automation platform OTP/password reset for external users Dedicated transactional platform External bulk email Dedicated bulk email provider HVE and the Mailbox External Recipient Rate Limit Cancellation Microsoft also announced that the Mailbox External Recipient Rate Limit in Exchange Online was cancelled indefinitely. However, that cancellation should not be interpreted as permission to use Exchange Online for uncontrolled bulk sending. Microsoft was clear that other limits remain unchanged, including the existing Recipient Rate Limit and the Tenant-level External Recipient Rate Limit. That distinction is important. The cancellation of one mailbox-level external recipient limit does not remove the need for proper architecture. Exchange Online still has service limits. Outbound spam controls still apply. Tenant-level protections still matter. And HVE is still not a marketing engine. Practical Architecture Decision Before enabling HVE, ask these questions: Who is sending? Is the sender a human, shared mailbox, application, or device? Who are the recipients? Are they internal or external? What is the expected volume? Is the workload operational, transactional, promotional, or human communication? Does the business need Microsoft 365 mail flow and governance? Does the use case require bounce handling, unsubscribe, tracking, or reputation management? Is the application properly authenticated and monitored? Who owns the account? Who approves the sending pattern? Who responds if the account is abused? If the workload is internal, automated, high-volume, and business-approved, HVE may be the right answer. If the workload is external, promotional, customer-facing, or marketing-driven, use a dedicated email delivery platform. Recommended Enablement Approach Organizations should enable HVE in phases. First, identify existing systems currently using user mailboxes, shared mailboxes, or SMTP AUTH for automated sending. Second, classify each workload as internal, external, operational, transactional, marketing, or human communication. Third, migrate only approved internal high-volume workloads to HVE. Fourth, move external high-volume workloads to dedicated email delivery platforms. Fifth, monitor usage and review HVE accounts regularly. This avoids turning HVE into another uncontrolled sending layer. Conclusion High Volume Email for Microsoft 365 is an important addition to Exchange Online. It gives organizations a native way to support high-volume internal system messaging without using standard mailboxes for automated high-volume traffic. But HVE is not a free pass for bulk email. It is not a marketing platform. It is not a replacement for transactional email services. And it should not be enabled for every mailbox or every application. The right approach is workload classification. Use Exchange Online for corporate communication. Use HVE for approved high-volume internal system messaging. Use dedicated platforms for external bulk, marketing, and transactional email. The question is not only: “Can this system send email through Microsoft 365?” The better architectural question is: “What type of email is this, who is the audience, and what is the correct platform for this workload?” That is where proper email architecture begins.
Exchange on-prem license
Hello, I have installed ExchangeServerSE x64 iso file its in trial version i want to license it. What kind of license do i need? I have the following information from the EAC: Version 15.2 (Build 2562.17) Standard Trial Edition Trial and from powershell: Edition : StandardEvaluation AdminDisplayVersion : Version 15.2 (Build 2562.17) Since i've installed the ExchangeServerSE x64 is this the correct license i should require? Exchange Server Subscription Edition (SE) license 5 × Exchange Server Standard CALs (one per user/mailbox) Environment details: Exchange version: 2019 (Version 15.2) Number of mailboxes: 5 Is this valid and the correct license? Kind regards, Filip M
Gmail to Microsoft 365 Migration Issue Open for 7+ Days – Seeking Guidance or Escalation Path
I’m facing an issue with a Gmail to Microsoft 365 migration that has been open for more than 7 days, and I’m looking for guidance or an escalation path from the community. Scenario: Migration type: Gmail to Microsoft 365 Issue started: April 22 Current status: Stuck with no clear resolution What’s happening: The support ticket has been active since April 22. However, the updates I’ve been receiving are generic responses such as “we are working on it” and “this has been prioritized.” Despite multiple follow-ups, there has been: No clear root cause identified No ETA provided No technical breakdown of the issue I also requested a callback from the assigned manager and technical lead to better understand the situation, but the communication has remained email-only with repeated status updates. What I’m looking for: Has anyone faced similar issues during Gmail → Microsoft 365 migrations? Are there known blockers or common causes that could lead to this kind of delay? What is the recommended escalation path when support is unable to provide technical clarity or ETA? Any insights, workarounds, or guidance would be highly appreciated. Thank you in advance.
User cannot rename categories even when being the owner
Hi guys, I have a user that cannot rename categories in a mailbox whilst being the owner. As you can her permission level is set on owner. And yet the rename is greyed out: User says she was able to rename just some time ago, but when she tried on 17/04/2026 she couldn't. Anyone has any ideas?
ARC verification fail (40) on specific Exchange Online frontends - recurring issue
Hello, We are observing recurring arc=fail (40) errors on messages forwarded through Exchange Online, caused by specific frontend servers. The same messages pass ARC verification correctly on other providers (Google, etc.). Affected frontends identified so far: CH2PEPF0000013F.namprd02.prod.outlook.com - build 15.20.9700.17 (March 14, 2026) CH3PEPF0000000B.namprd04.prod.outlook.com - build 15.20.9769.17 (April 6, 2026) Both share the same build suffix .17. The signing implementation on our side has been cryptographically verified as correct and RFC 6376 compliant. The issue has also been reported on the IETF ietf-smtp mailing list with full technical analysis. Cryptographic analysis shows the failing servers append a spurious trailing \r\n to the last header before computing the verification hash, violating RFC 6376 Section 3.7. Is there a pattern with .17 frontend builds and ARC verification? Reagards VittorioMailbox for Service Account (exchange online)
Hi Our organisation isn't ready to move to Exchange Online yet, though we have Office 365 e3 licencing. I need to create a service account that can send emails via Outlook 365 for use In Power Automate. The documentation I have seen for adding a mailbox to an existing AAD user requires assigning an exchange licence to the account via the licence portal. I can't see any such licences though we do have e3 licencing which are visible that I assume covers this? Unfortunately the admin who did the original configuration has moved on and I don't have a global admin role so have to go through a support team that can't help me with my lack of knowledge in the area! Any advice would be very much appreciated as what ( i think) should be a simple task has taken a lot of time to try and get to the bottom of! Thanks, Dale.
