TS-022: Shared mailbox opens but cannot send from it

Resolved an Exchange Online shared mailbox fault in which the user retained Full Access but could not send as the mailbox. Service Desk isolated the permission gap, escalated the privileged change and validated successful delivery before closure.

Scenario

Kate Jones could open the Sales shared mailbox but could not send messages from [email protected]. This indicated that mailbox access and sending permissions needed to be checked separately.

Priority reasoning: Impact was set to 3 - Low because one user was affected. Urgency was set to 2 - Medium because the user retained mailbox access but could not perform the required Send As function. Under the priority matrix, this produced 4 - Low.

ServiceNow Ticket

The incident was assigned to Chloe Bennett in the Service Desk and classified using the relevant service records:

ServiceNow incident INC0010080 showing Microsoft 365 and Exchange Online classification, service records, P4 priority and assignment to Chloe Bennett
Figure 1The incident was opened with the correct Microsoft 365 service classification, Exchange Online configuration item and Service Desk ownership.

Investigation

Chloe checked the Sales shared mailbox delegation settings. Kate was present under Full Access, which explained why she could open and read the mailbox.

Exchange Online mailbox delegation showing Kate Jones under Full Access
Figure 2Kate Jones had Full Access permission, confirming that basic mailbox access was working.

The separate Send As list did not contain Kate. This isolated the fault to the permission required to send messages using the Sales mailbox address.

Exchange Online mailbox delegation showing Kate Jones missing from Send As
Figure 3Kate Jones was missing from the Send As delegation list.

The issue was reproduced in Outlook on the web. A test message sent from the Sales mailbox returned a clear permission error.

Outlook on the web showing a permission error when sending from the Sales shared mailbox
Figure 4Outlook on the web confirmed the user-facing Send As failure before remediation.

Fix Applied

Changing shared mailbox delegation was outside the first-line Service Desk permission scope. Chloe documented the completed checks, recorded the missing Send As permission and reassigned the incident to Kristian Nietzold for the privileged Exchange Online change.

ServiceNow incident INC0010080 showing Chloe Bennett's investigation and reassignment to Kristian Nietzold
Figure 5Chloe recorded the evidence, identified the permission gap and escalated the incident for privileged administration.

Kristian added Kate Jones to the Sales mailbox Send As delegation list. Existing Full Access permission was left unchanged, and the incident was returned to Chloe for user retesting and closure.

Exchange Online mailbox delegation showing Kate Jones added to Send As
Figure 6Send As permission was restored for Kate Jones on the Sales shared mailbox.

Validation

A fresh validation message was sent from [email protected] to [email protected]. Exchange message trace showed that the message was received, processed and delivered successfully. Kate then confirmed by phone that she could send successfully from the Sales address.

Exchange message trace showing the Sales shared mailbox validation message was delivered successfully
Figure 7Exchange message trace provided independent evidence of successful Send As delivery after the permission change.

Resolution

Chloe resolved the incident using Solution provided. The resolution notes recorded the original permission mismatch, escalation, privileged change, successful message trace and Kate's confirmation by phone.

ServiceNow incident INC0010080 showing Solution provided, Chloe Bennett as resolver and completed resolution notes
Figure 8The incident was resolved with a clear audit trail of investigation, escalation, remediation and validation.

Summary

  • Classified a shared mailbox incident using the correct ServiceNow service, offering and configuration item.
  • Distinguished Full Access from Send As permission.
  • Reproduced the user-facing error in Outlook on the web.
  • Documented the first-line findings and escalated the privileged permission change through the approved support path.
  • Restored Send As permission without changing existing Full Access.
  • Validated the fix with a fresh Exchange Online message trace and user confirmation by phone.
  • Resolved the incident with clear, auditable resolution notes.
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