Most probable issue is an issue with the libraries in the lib directory of your project.
Either there are duplicate jar files with a different version number for example, or you are missing libraries.
I’d would start there to find the solution.
Kindly go through the prerequisites mentioned in the email connector documentation: https://docs.mendix.com/appstore/connectors/email-connector/?_gl=1*1ulcak5*_ga*MTc2NjY1MjAxMC4xNjg1NjE0NTA3*_ga_4PE2C4QFC7*MTY4Njg5MTg4OC4zMy4xLjE2ODY4OTQyMDguNTMuMC4w#12-prerequisites
Also can you please let me know about the other modules and their versions that are present in your project apart from email connector.