When a mail should be sent an exception is thrown:
org.springframework.webflow.execution.ActionExecutionException: Exception thrown executing [AnnotatedAction@2282ab51 targetAction = [EvaluateAction@30bd648a expression = groupApplicationAction.processSubmit(flowRequestContext), resultExposer = [null]], attributes = map[[empty]]] in state 'groupApplicationSubmitted' of flow 'groupApplication-flow' -- action execution attributes were 'map[[empty]]'
...
Caused by: ognl.MethodFailedException: Method "processSubmit" failed for object [GroupApplicationAction@ae9ecc8 formObjectName = 'groupApplicationCommand', formObjectClass = GroupApplicationCommand, formObjectScope = Flow] [java.lang.ArrayIndexOutOfBoundsException: 0]
        at ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1265)
...
Caused by: java.lang.ArrayIndexOutOfBoundsException: 0
        at sgf.gateway.service.security.impl.spring.EmailServiceImpl.send(EmailServiceImpl.java:109)
...

This are the parameters which are correctly set (at least they worked on a different gateway with the previous version):

# email.server.address : esg-admin@albedo2.dkrz.de
# email.server.host : localhost
# email.server.password :
# email.server.port : 25
# email.server.username :