With Buttondown's RSS-to-email functionality, you can have Buttondown aggregate posts from your RSS feed in daily, weekly, or monthly increments, then sending one email with all those posts.
Buttondown checks your RSS feed every hour, and when it finds new posts for the current month, it appends them onto a draft (marked with an "Automated" status).
Finally on the day you choose under "Schedule," the previous month's draft is finalized (and sent, if you chose this Behavior).
Let's say you publish posts to your RSS feed on these dates:
Throughout January, a draft will be created with the posts from January.
Once January is over, the January draft is finalized, and the February 1 post is added to a new draft for February.
Then, on the correct day in February (i.e. first Monday, or whichever is chosen under Schedule), the January email is sent out.
When you send a test email to yourself, the behavior is a bit different:
Buttondown takes all the posts in the current month and compiles them into a test email, which it sends to the email address on file for your account.
This is meant more as a way to preview your template to make sure everything's working, not to emulate the usual process of compiling posts over the course of a month.
When your automation's cadence is set to Weekly, the same logic applies, just from one week to the next instead of one month to the next.