Unable to send emails in new Outlook for Mac

Products

• Cloud Secure Web Gateway - Cloud SWG

Issue/Introduction

You are using the 'new Outlook' feature in Outlook for Mac. 

When you send an email, it does not leave the outbox.

There are no issues if you revert to legacy Outlook mode or use web version of Outlook. 

Environment

Affected Outlook for Mac version: 16.89

WSS Agent

Cause

CloudSWG reporting shows verdict invalid__request for https outlook.office365.com 443 /outlookservice/servicechannel.hxs

Only the new Outlook mode on Mac Outlook is affected by this issue.

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invalid_request DENIED "Business/Economy;Email" - 400 TCP_NC_MISS_RST POST application/httpsocket.wbxml https
outlook.office365.com 443 /outlookservice/servicechannel.hxs

Resolution

This can be addressed with the following CPL:

<proxy>

url.prefix=https://outlook.office365.com http.response.response_data.prevent_inspection_delay(yes)

In order to implement this, reach out to Support to have Engineering add this to your policy.