Is it possible to set in the Graylog custom email address, which will be changed by the new value of an Event?

Hello && Welcome @Jana

Good question, So let me see if I understand this correctly.

If an event is triggered, you want a group email account for all these users?
or want to auto-mat something for a specific user when a certain event is triggered?

if your referring to a Field within the message that has a user email, then yes.
On the other hand if your trying to insert a users name with domain account, I haven’t seen that done yet.
Creating a stream then attaching the notification template you can use either User recipient(s) and/or add Email recipient(s) . Normally the Email recipient(s) may not be a member of the organization or domain.

Example:

Perhaps you looking for something like this.

My apologies I don’t have a direct answer.