A simple App raises this error. I make use of mail package. From java documentaion I undertstand it may by a classpath problem. Any suggestions how to deal with this error? ava.lang.NoClassDefFoundError: org/apache/commons/mail/EmailException at emailtemplate.actions.SendEmail.executeAction(SendEmail.java:133) at emailtemplate.actions.SendEmail.executeAction(SendEmail.java:25) at com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:53) at com.mendix.core.actionmanagement.CoreAction.doCall(SourceFile:291) at com.mendix.core.actionmanagement.CoreAction.call(SourceFile:276) at com.mendix.core.actionmanagement.ActionManager.executeSync(SourceFile:205) at com.mendix.core.component.InternalCore.execute(SourceFile:259) at com.mendix.hs.execute(SourceFile:42) at com.mendix.ib.a(SourceFile:47) at com.mendix.ia.a(SourceFile:193) at com.mendix.ia.executeAction(SourceFile:148) at com.mendix.systemwideinterfaces.core.UserAction.execute(SourceFile:53) at com.mendix.core.actionmanagement.CoreAction.doCall(SourceFile:291) at com.mendix.core.actionmanagement.CoreAction.call(SourceFile:276) at com.mendix.core.actionmanagement.ActionManager.executeSync(SourceFile:205)