I haven't found a better place to report a bug in the "Microsoft Junk E-mail Reporting Add-in for Microsoft Outlook".
The add-in sends the message not from the current mail account but rather from the primary/default (which in my case is not an Office 365 but my business email).
I would appreciate if this bug could be addressed.
The add-in works per account, you should not even see it enabled for accounts that are not O365 accounts. Are you perhaps referring to the old add-in (as in not the one described here: https://support.office.com/en-us/article/use-the-report-message-add-in-b5caa9f1-cdf3-4443-af8c-ff724...)?
Do you happen to have the "Always use the default account when composing messages" option enabled?
I've been using Microsoft Junk E-mail Reporting Add-in for Microsoft Outlook®: https://www.microsoft.com/en-us/download/details.aspx?id=18275 - as advised in a recent Ticket #:7354130.
I'll remove it and use the version you suggested.
Uninstall seems broken: I get an error from msiesxec.exe:
Windows cannot access the specified device, path or file. You may not have the appropriate permissions to access the item. (when running from Settings, Apps&features).
I'll disable the addin in Outlook