@SK
Thank you for your post!
Based off my knowledge with AIP for Outlook, content marking is only applied after Exchange Online sends the email. If the plugin crashes before-hand it makes sense that the email should be waiting for the label to be applied before it successfully sends.
Additional links:
Sensitivity label capabilities in Outlook
Should you deploy the Azure Information Protection unified labeling client?
As of right now, I'm not aware of any security and compliance center feature that will allow emails in case a plug-in fails. However, if you'd like this feature to be implemented, I'd recommend posting on our User Voice forum so our engineering team can look into implement this. Lastly, you can leverage our Yammer site for Azure Information Protection AIP since this resource provides direct responses from the Azure Information Protection team.
If you have any other questions, please let me know.
Thank you for your time and patience throughout this issue.
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