I have 

Xeams Community Edition Version 5.3, build 5863.

It's look a like installation kit is broken, some files missing like /share/CACHEDEV1_DATA/.qpkg/QXeams/Xeams/config/config/UserConfig.xml

Yesderday I install your version to QNAP  and everything works fine, today I need to reinstall everything and after than I got lot off problems. That's not normal if use same installation set!

I also test install other email server and they not work either. I know that google doing something under it's not the first time.

Why there is com.google... java parts?

2020-10-25 20:00:05,701 ERROR [localhost].[/] - Exception while dispatching incoming RPC call
com.google.gwt.user.client.rpc.SerializationException: Type 'com.synametrics.livemonitor.shared.LiveMonStatusHolder' was not assignable to 'com.google.gwt.user.client.rpc.IsSerializable' and did not have a custom field serializer.For security purposes, this type will not be serialized.: instance = com.synametrics.livemonitor.shared.LiveMonStatusHolder@397d61cb
at com.google.gwt.user.server.rpc.impl.ServerSerializationStreamWriter.serialize(ServerSerializationStreamWriter.java:667)

I fix than to add /etc/hosts

127.0.0.1 localhost REAL_HOSTNAME_HERE