PostMaster-Filter: How to set emails as internal when customer is not in the loop?

[SarahH]

Hi everybody,

sometimes we have internal communication within a ticket, e. g. our sales agent gives me a note, without adding the customer to the mail.
The privous outgoing mail was set as "external", so when the agent answers, it is marked as "external", too.

So, I set a postmaster filter, but the result is, that all new tickets are marked as internal.
I tried different notification tags (e. g.<OTRS_TICKET_CustomerUserID> which consists of the email address), without success.

Please see the screenshot, which shows my current config.

Has anybody realized this before and can help me or send me his config?
Thank you!