I am trying to connect to an external mysql DB using the Database Replicator with the following settings: Since there is no support for mysql database, I am using custom settings. Connection string: jdbc:mysql://localhost:3306/northwind Driver Class: com.mysql.jdbc.Driver Username and passowrd and getting the below error. I tried putting the mysql jar file in the Mendix\App\userlib folder but still got the same error. Error Message: com.mysql.jdbc.Driver not found by project 
Simply adding the jar file is not enough. These are complex database mappings and it will need more custom code besides just the right jar to make this work.
You'll have to either implement it yourself or file a support ticket with Mendix for this.