Hi, we have been using the email listener for a few weeks now but since putting

It could be they don't have the right routing information. Add these lines to any location to your appian_log4j.properties (<APPIAN_HOME>\\runtime_ear|ear\\suite.ear\\resources\\) they will give you more information on what's going on.

log4j.logger.com.appiancorp.messaging=DEBUG
log4j.logger.com.appiancorp.process.execution.service.ProcessExecutionServiceFacade=DEBUG
log4j.logger.com.appiancorp.mdb=DEBUG

These lines in conjunction with DEBUG mode in the ejb-jar.xml should give you more detail on what the problem is (look at the server.log)

You will also see errors in the application server log if the picked up emails do not have routing information. ("process/model id does not exist"

Thanks both, I have added the logging to our UAT environment and will be getting the emails sent to my test environment so I can analyse the errors further.

The eMails are getting picked up though as I am getting an alert. Without pasting the entire error due sensitive data the issue I am getting is ...

ERROR:EVAL:@reason=Invalid index: Cannot index into

There is still more of this error message that can be provided without exposing sensitive information. At a glance this error looks of type:
"EVAL:@reason=Invalid index: Cannot index property 'XXXXX' of type Y into type YYYY".

If that is the case then it seems the process is trying to retrieve a field from a CDT which is null, something like pv!myCDT.myField where pv!myCDT is null (No Value) which results in an invalid expression of type null.myField