Hi,
when running locally you might need to clean your deployment directory to remove old .jar files there too.
Have you tried that?
Following the instructions in the Prerequisites of the Email Connector module worked for me:
As I had to migrate the data from the Email Template module to the Email Connector module I could not delete the Email Template module. Instead, I deleted all the jar-files related to this modules in the userlib as well as the subfolders for the Email Template module in the folders javasource and javascriptsource, after ensuring that there was no use of the module anymore in the model. After downloading the relevant modules again (Email Connector, Encryption and Model Reflection) once again and cleaning up the userlib for older versions of the jar-files, the email connection worked.
The Email Connector module should include all the .jar files it needs. If you download jars from another location you could be downloading the wrong version and seeing errors like the one you describe in your question.
I would suggest removing the .jar files you downloaded from elsewhere and just reinstall the Email Connector module directly from the Mendix Marketplace in Studio Pro.
I hope this helps.