Welcome to the community ​@Karen K 

If I understand your use case correctly:

1. You want to send a monthy newsletter that is new, original content each month to your newsletter subscribers. I would send that email via a scheduled campaign each month to your current newsletter subscribers. 
2. You want to send the current newsletter to your subscribers as they join your list if that’s after it’s been sent as a campaign and before next month’s is sent. I would create a list or segment-triggered flow so new members receive the current newsletter. Notify them in that email that they will receive your next newsletter on the 1st of each month (for example). You will need to update that flow email each month so it is your latest newsletter. Create your latest newsletter as a template and then apply that template to your flow email step.

So new subscriber members will immediately receive the current newsletter via the flow. ALL subscriber members will receive the next newsletter via a campaign on the 1st of the month. 

If you want to avoid the overhead of updating the flow email each month, you could just send new subscribers a confirmation “thanks” and “look out for your first newsletter on the 1st”.

Alternatively you could include in that flow email an evergreen link to a web page that lists all your historical newsletter content. Just update that web page and the flow email can remain unchanged

Does that help?

Regards

Andy   

Thank you Andy that's a great help.

Karen