2022-Mar-03 20:49 UTC (2022-Mar-04 07:49 AEDT): Microsoft are claiming the issue has been fixed and that the fix is being rolled out. Janusnet have confirmed the fix seems to be present in Australia and that it rectifies the issue.
The issue was recorded as an incident in the Microsoft 3565 admin center > Health > Service Health ; ID = EX337976 "Some users were unable to send email via the on-send feature for Outlook add-ins in Outlook on the web" (at the time of writing is visible under the History tab)
When a user tries to send a message from Outlook on the Web (OOTW), the Janusseal App classification dialog is shown, but after the user selects a classification the Send (or Cancel) button does not do anything and the message is not sent.
Appears to be related to this new issue being reported to Microsoft - Not possible to close the dialogs. The dialog.close() API is broken. · Issue #2457 · OfficeDev/office-js (github.com)
Microsoft have posted the following to the github ticket
We (Microsoft Engineers) are working on this issue. It will be fixed soon
This issue might only be affecting those customers that are on the Current Channel of Microsoft 365.
Nothing has changed in the Janusseal App for Outlook codebase; Microsoft must have changed something in the OOTW code to cause this issue.
Janusnet and others have reported the issue to Microsoft at Issues · OfficeDev/office-js (github.com) and are awaiting a response.
We do have a potential emergency code fix we could roll out, but it does introduce a second pop-up that end-users have to click and we do not necessarily want to roll out this fix if not all our customers are affected.
For some customers, it might be possible to classify the item before sending by using the compose mode side pane - the user clicks the Janusseal App "blue triangles" icon and specifies a classification in the side pane before clicking the Send button:
This is only a viable workaround if your organisation's Janusseal App for Outlook configuration is such that the user does not have to confirm the message's classification upon sending. Janusnet could adjust your organisation's configuration to turn off confirmation, if required, to make use of this temporary workaround.