@AB1 :
You can use a recurrence trigger to run a Flow periodically such as every X number of months.
Assuming that you have a list of people to whom you want to send emails, you can loop them each one and attach a unique attachment assuming that there is a link of some type between the attachment and the email address. In other words you need to be able to identify what attachment goes with what email. The attachments need to be accessible to Flow - having them in a SharePoint library would work.
If you can be more specific, I can provide additional detail.
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Scott
