Error Running Process Model: Could not prepare email for: CompatibleEmailRecipients

Hello,

we are running a Process Model on On-Premises installation of Appian. We don't want to send notification via Email so we don't want to to start a mail service.
But we have this error in  unattended-request-poller.log

2019-04-29 06:51:16,196 [ThreadPoolTaskExecutor-22] ERROR com.appiancorp.process.workpoller.WorkItemListener - The following exception occurred while attempting to complete work item [(WorkId: 7, WorkType: MailRequest{subjectWithoutPrefix=Error in Task of Process., subject=, body=MailBody{filename=/ntf/emailHtml/taskException_emailHtml.jsp}, from=appian-alerts@ip-10-0-1-177, toUsernames=[Administrator], to=}, Response: null, ServerName: notifications-email)] - Exception:
javax.resource.spi.work.WorkCompletedException: java.lang.RuntimeException: Could not prepare email for: CompatibleEmailRecipients{locale=en_US, timeZone=Europe/Rome, calendarId=gregorian, startPage=democenter, emailAddresses=[example@mail.com}
at org.springframework.jca.work.SimpleTaskWorkManager$DelegatingWorkAdapter.run(SimpleTaskWorkManager.java:242)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.RuntimeException: Could not prepare email for: CompatibleEmailRecipients{locale=en_US, timeZone=Europe/Rome, calendarId=gregorian, startPage=democenter, emailAddresses=[exampe@mail.com]}
at com.appiancorp.process.engine.AbstractMailRequest.execute0(AbstractMailRequest.java:238)
at com.appiancorp.process.engine.ContinuationRequest.executeOuter(ContinuationRequest.java:71)
at com.appiancorp.process.engine.ContinuationRequest.execute(ContinuationRequest.java:90)
at com.appiancorp.process.workpoller.UnattendedRequestHandlerBean.onMessage(UnattendedRequestHandlerBean.java:35)
at com.appiancorp.process.workpoller.WorkItem.run(WorkItem.java:84)
at org.springframework.jca.work.SimpleTaskWorkManager$DelegatingWorkAdapter.run(SimpleTaskWorkManager.java:239)
... 3 more
Caused by: com.appiancorp.process.engine.EmailBodyException: Email body failed to render: MailBody{filename=/ntf/emailHtml/taskException_emailHtml.jsp}
at com.appiancorp.process.engine.MailRequest.renderEmailBody(MailRequest.java:92)
at com.appiancorp.process.engine.AbstractMailRequest.execute0(AbstractMailRequest.java:226)
... 8 more
Caused by: java.net.ConnectException: Connection timed out (Connection timed out)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at sun.net.NetworkClient.doConnect(NetworkClient.java:180)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
at sun.net.www.http.HttpClient.<init>(HttpClient.java:242)
at sun.net.www.http.HttpClient.New(HttpClient.java:339)
at sun.net.www.http.HttpClient.New(HttpClient.java:357)
at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1220)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1156)
at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1040)
at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1038)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessController.doPrivilegedWithCombiner(AccessController.java:782)
at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1037)
at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:984)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1564)
at sun.net.www.protocol.http.HttpURLConnection.access$200(HttpURLConnection.java:91)
at sun.net.www.protocol.http.HttpURLConnection$9.run(HttpURLConnection.java:1484)
at sun.net.www.protocol.http.HttpURLConnection$9.run(HttpURLConnection.java:1482)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessController.doPrivilegedWithCombiner(AccessController.java:782)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1481)
at java.net.URLConnection.getContent(URLConnection.java:739)
at com.appiancorp.process.engine.MailBody.renderBody(MailBody.java:205)
at com.appiancorp.process.engine.MailRequest.renderEmailBody(MailRequest.java:90)