The documentation at Setting Up a Mail Session for the Confluence Distribution needs to be updated for version Confluence Server 7.20
The files for step 2 have changed.
It is *jakarta.activation-x.x.x.jar* instead of *javax.activation-x.x.x.jar*
And the file *javax.activation-api-1.2.0.jar* does not exist any longer, so it does not need to be moved.
I would be happy if you update this documentation.
Additionally the feedback form on the documentation page did not work for me with the following error:
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There was a problem submitting your feedback, likely due to the configuration of this form. You might want to contact the site owner to let them know about this issue.