Zammad: Ticket gets reopen by an email send via a trigger configured with recipient article_last_sender and article sender was 'customer'

Infos:

• Used Zammad version: 2.9
• Installation method (source, package, ..): any
• Operating system: any
• Database + version: any
• Elasticsearch version: any
• Browser + version: any

Expected behavior:

• Zammad should not reopen tickets by sending a trigger notification to Zammad it self.

Actual behavior:

• In certain cases Zammad sends a trigger base email notification to Zammad it self and my reopen the ticket.

Steps to reproduce the behavior:

• create trigger #1 with

  • state is changed
  • trigger notification to article_last_sender

• create trigger #2 with

  • state is changed
  • trigger notification to article_last_sender

• close a ticket and you will see 2 trigger based notifications. The second one is sending a email to Zammad it self (because the used article_last_sender is based on first generated trigger based email notification).