Microsoft 365 Alert – Service Degradation – Exchange Online – Some users may intermittently be unable to access their mailboxes using Internet Mailbox Access Protocol 4 (IMAP4) – RESOLVED

Announcements Arpan Das

08/01/2025 09:03:00 AM

NHSmail Reference: INC46719151

Microsoft Reference: EX1215307

Issue Status: RESOLVED

Issue Description: Users may intermittently be unable to access their mailboxes using IMAP4.

More info: Impact is specific to IMAP4, other connection methods are not impacted. Additionally, if users are actively facing this issue, retries may be successful..

Final Update: 09/01/2026 07:56:00 AM – Microsoft has completed deploying the configuration change on the affected servers, which reduced volume and restored normal service functionality. After a period of monitoring, they have confirmed that impact has been fully remediated.

Scope of impact: Some users that are attempting to access their mailboxes using IMAP4 may be intermittently impacted. This information may be updated as our investigation continues.

Root cause: A recent IMAP deployment related to authentication support contains a code conflict that introduced a configuration issue and is causing intermittent mailbox access issues for some impacted users.

Next Steps: Microsoft are reviewing their deployment and provisioning procedures to help prevent similar problems in the future.