I get frequent complaints from libraries about patrons getting emails saying their items can't auto renew. The typical error message is "too_many", and it's sent every single day. Most of the time, we probably only want to send email notices out when the item has successfully renewed. Then notices like advanced item due, item due, and overdues take over from there.
(On a side note, the precedence of errors in automatic renewals makes no sense. In the most common scenarios, you'll probably never see an "overdue" because you'll get "too_many" first.)
Since people will disagree on this one, we would wrap it in a system preference anyway.
This one might not be valid anymore... as I think the auto renewals logic has improved a lot over the last year...
Auto-renewal logic has changed a lot but there still are many challenges. Yes, ‘pointless emails’ are a problem (bug 35656 doesn’t help!). But we want the opposite of what is suggested here. Our patrons are told the items will renew 9 times (for ten 1 week loan periods) and we want to email them only if that routine is stopped. Ideally the development direction auto-renewals takes generally will offer choice, so the customer can select preferred functionality. Koha administrators have subtly different expectations for how auto-renewal should work. The functionality is puzzling at times, for example with potentially duplicate emails from different notices (see bug 38203). And our 23.11 still sends digests for the too_many error as well as the auto_renewal_final one but we are delighted it does despite what bug 34924 says. Yes, we have multiple too_many (and other DGST emails duplicated) but that is down to bug 35656. In the absence of a product manager who defines the LMS roadmap, getting agreement as to what should be ‘standard auto-renewals functionality’ is always going to be a challenge that open-source Koha faces.