Thanks, @rhawbert 
I never heard of Mandrill, but it appears to be a more direct approach than MailChimp itself.
I (tried to) develop this Kirby integration, just because of privacy concerns of the customer (a.k.a. friend of mine).
He preferred the direct integration, without having to hand over the newsletter recipients email addresses to a ‘third party’.
That’s a little bit of a paranoia, since they use gmail ever since, but who am I to judge? 
In addition: any mail-footer-advert is not acceptable.
The Mandrill approach is more reliable, though. To be totally honest, I have my concerns of sending the emails via php scripts in the background, because one does not have any control of aborting, etc. the process.
What came up my mind in the last few days of intense Kirby-forum-time:
- have a widget to start sending emails, as @FabianSperrle proposed earlier
- perhaps adapting a list of posts via @DieserJonas’ panel field extension (select post to send via mail)
- have recipients integrated into Kirby as users
- create a subscribe/unsubscribe form
@FabianSperrle created a small widget on github, which should make it easier for me learning the widget stuff (and it’s cat content!!)
this is rough, since I am a php noob.
And I have no idea on how to control the process that is sending mails.