Added protocol hint

app/src/main/java/eu/faircode/email/EmailService.java

@@ -73,6 +73,8 @@ import javax.mail.event.StoreListener;
 import javax.net.ssl.KeyManager;
 import javax.net.ssl.KeyManagerFactory;
 import javax.net.ssl.SSLContext;
+import javax.net.ssl.SSLException;
+import javax.net.ssl.SSLHandshakeException;
 import javax.net.ssl.SSLSocket;
 import javax.net.ssl.SSLSocketFactory;
 import javax.net.ssl.TrustManager;
@@ -369,6 +371,15 @@ public class EmailService implements AutoCloseable {
         } catch (MessagingException ex) {
             if (port == 995 && !("pop3".equals(protocol) || "pop3s".equals(protocol)))
                 throw new MessagingException(context.getString(R.string.title_service_port), ex);
+            else if (ex.getMessage() != null &&
+                    ex.getMessage().contains("Got bad greeting"))
+                throw new MessagingException(context.getString(R.string.title_service_protocol), ex);
+            else if (ex.getCause() instanceof SSLException &&
+                    ex.getCause().getMessage() != null &&
+                    ex.getCause().getMessage().contains("Unable to parse TLS packet header"))
+                throw new MessagingException(context.getString(R.string.title_service_protocol), ex);
+            else if (ex.getCause() instanceof SSLHandshakeException)
+                throw new MessagingException(context.getString(R.string.title_service_protocol), ex);
             else
                 throw ex;
         }

app/src/main/res/values/strings.xml

@@ -643,6 +643,7 @@
     <string name="title_hint_alias">Long press an identity to display options, like copy to create alias identities</string>
     <string name="title_service_vpn">This might be caused by the VPN that is being used</string>
     <string name="title_service_port">Please double check the port number</string>
+    <string name="title_service_protocol">Please double check the protocol (SSL/TLS or STARTTLS)</string>
 
     <string name="title_advanced_browse">Browse messages on the server</string>
     <string name="title_advanced_expand_read">Mark messages read on expanding</string>