You can use our Updates & Newsletters feature or mailing list integration to deliver paid-subscription issues to your buyers. We'll need to manually enable "soft opt-in" for the product -- i.e., a subscription opt-in implicit by the fact they chose to purchase a subscription product -- to ensure that all buyers of the product are subscribed to receive periodic delivery of their purchased content without requiring them to manually tick a box to opt-in during/after checkout.
Delivering periodic Stamped PDF files
If you set up an e-magazine product that delivers a PDF file protected with PDF Stamping, all download links we issue for that product would apply Stamping -- whether a purchased link or any free links you issue manually or via a mass-email Update to previous buyers. Whenever you have a new issue to distribute, you'd simply upload the new PDF file to the existing product, then send an Update to previous buyers. If your subscriptions will expire -- e.g. a year after the buyer's latest purchase -- you can remove expired buyers before sending the Update, via Manage Buyers > View/Edit Email Lists in your Seller Admin.
Every link for a Stamped PDF would always download the same Stamped copy from when that link was first issued, for up to a year after the link was generated. Thus, buyers could re-use their links to re-download their first issue and each subsequent issue they received via Updates within the past year, as long as the link isn't expired. You may wish to leave the Hours expiry setting blank/0 in your product settings, so links would only expire when their max. Attempts have been reached, or the one-year Stamped PDF archive limit has been reached (whichever comes first). In case a buyer loses their link, you can always obtain it from your Transaction Log (for purchased links) or your Free Downloads Log (for free links sent manually or via Updates).