@mpfischer,
Thank you for your question.
Unfortunately MailPoet 3 does not provide such feature directly, however depending on your use case you may still be able to achieve a similar result.
What you could try is preparing a newsletter with your intended message (just a one time email sent to your subscribers), and schedule it to be sent at your next intended date.
Then duplicate the email, change the message if you desire, and reschedule the duplicated email for the next time you would like it to be sent (e.g. 3 months after the first one).
That way if you want to send a fixed message to your subscribers every 3 months for a year – that would mean creating 4 newsletter emails and scheduling them to be sent in 3 month intervals.
As an added benefit, you will have the option of specifying the exact days you’d like the email to be sent.
Not the ideal solution to your problem, but it might work just well enough.
As @lynnmonk has mentioned though, such approach will need some upkeep, but such emails could be scheduled once in batches and forgotten for a longer period of time.
@mpfischer and @lynnmonk, thank you both for your valuable input. At the moment, unfortunately, our priorities are elsewhere, so I cannot promise its implementation any time soon, but we are noting down your feedback for future improvement considerations.
Thanks!
Best regards,
MailPoet Team.