we are having problems getting our taskException emails to render after upgrade

Those settings will work, but per the documentation they need a double restart of the engines. Just restart the engines twice.

conf.suite.MAIL_SCHEME=httpconf.suite.MAIL_SERVER_AND_PORT=localhost:8080




Should this be localhost or the server name?

depends on your topology, both work given certain assumptions. if you are single host topology, localhost is more logical.

I am now getting this error:-
Caused by: java.net.SocketException: Unexpected end of file from server
I am not using localhost and my App Server port is different

Basically these settings should point to your APP_SERVER whatever its name is and whatever port it's using

conf.suite.MAIL_SCHEME=http
conf.suite.MAIL_SERVER_AND_PORT=myappserver.mycompany.com:8080

Yes, that's what I am using

conf.suite.MAIL_SCHEME=http
conf.suite.MAIL_SERVER_AND_PORT=myserver.mycompany.com:21007

Only issue is that my App Server and my Web Server both are on the same box with just the PORT change from 21007 to 4511 and then Web Server and App Server both are HTTPS

Can you post the stack trace under the line

java.net.SocketException: Unexpected end of file from server

Caused by: java.net.SocketException: Unexpected end of file from server
          at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:772)
          at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:633)
          at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:769)
          at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:633)
          at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1323)
          at java.net.URLConnection.getContent(URLConnection.java:748)
          at com.appiancorp.process.engine.MailBody.renderBody(MailBody.java:101)
          at com.appiancorp.process.engine.MailRequest.renderEmailBody(MailRequest.java:63)
          at com.appiancorp.process.engine.AbstractMailRequest.execute0(AbstractMailRequest.java:135)

Caused by: com.appiancorp.process.engine.EmailBodyException: Email body failed to render
          at com.appiancorp.process.engine.AbstractMailRequest.execute0(AbstractMailRequest.java:140)
          at com.appiancorp.process.engine.ContinuationRequest.execute(ContinuationRequest.java:80)
          at com.appiancorp.mdb.UnattendedRequestHandlerBean.onMessage(UnattendedRequestHandlerBean.java:26)
          at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
          at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
          at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
          at java.lang.reflect.Method.invoke(Method.java:606)
          at org.jboss.as.ee.component.ManagedReferenceMethodInterceptor.processInvocation(ManagedReferenceMethodInterceptor.java:52)
          at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288)
          at org.jboss.invocation.WeavedInterceptor.processInvocation(WeavedInterceptor.java:53)
          at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:63)
          at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288)
          at org.jboss.invocation.WeavedInterceptor.processInvocation(WeavedInterceptor.java:53)
          at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:63)
          at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288)
          at org.jboss.as.ejb3.component.invocationmetrics.ExecutionTimeInterceptor.processInvocation(ExecutionTimeInterceptor.java:43)
          at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:288)
          at org.jboss.as.ejb3.tx.EjbBMTInterceptor.handleInvocation(EjbBMTInterceptor.java:104)
          ... 47 more