How to detect messages by Slack?

[GenieTim]

How can I detect messages such as "xy has joined the channel", "xy set the channel purpose", and similar, which are not really composed by a person but rather Slack? Unfortunately, the username and userId given in SimpleMessage are the same, no matter if its a message from a human being or Slack in the name of the human being. Is there a sensible way to detect what kind of message it is?

[GenieTim]

A workaround I found, in case anyone wonders about this too: If you do not give the application the rights to read the Usernames, the messages generally start with "<U" followed by some User ID. You can filter out all Messages beginning with this string to get rid of them...