Maybe there is a misunderstanding. The intention is not to use discourse as an “e-mail marketing plattform”. Both systems mentioned (discourse and the mailman mailing lists) are only used for an internal group of users (non-public).
We have a number of users that still do not use discourse for various reasons (e.g.because they think its “too complicate”, because they dont want to use a browser instead of an e-mail-client etc.). The intention is to use the activity e-mails as a “discourse appetizer”.
The goal is to make these users more open towards the usage of discourse. This could be achieved with a number of e-mails with interesting content and links from the discourse platform which are manually sent by moderators who have access to both the discourse instance and the old mailing lists.
The final goal is the migration of all users and their team communication to the discourse instance and the replacement of internal mailing lists.