When attempting to change the reply email address from Central Admin> Nintex Workflow Management>Lazy Approval Settings an error is generated.

Please refer to these two blogs and ensure the Central Web Application has sufficient permissions in active directory:

https://blogs.technet.microsoft.com/jks/2009/03/04/how-to-deal-with-an-error-in-configuring-incoming-e-mail-settings/

http://sharepointgeorge.com/2010/configuring-incoming-email-sharepoint-2010/ 
 

Application error when access /_layouts/15/NintexWorkflow/ManageApprovalAI.aspx, Error=Error in the application. at Microsoft.SharePoint.SPList.UpdateDirectoryManagementService(String oldAlias, String newAlias) at Microsoft.SharePoint.SPList.Update(Boolean bFromMigration) at Nintex.Workflow.Administration.LazyApproval.UpdateList(SPWeb web, SPList list, String alias, ConfigurationScope scope, String libraryName) at Nintex.Workflow.Administration.LazyApproval.<>c__DisplayClass3.b__0() at Microsoft.SharePoint.SPSecurity.CodeToRunElevatedWrapper(Object state) at Microsoft.SharePoint.SPSecurity.<>c__DisplayClass5.

The same error occurs when trying to change the reply email address for a Sharepoint library that has been enabled to receive emails.