O, so Quick Base does not let you send a regular overnight automatic Subscription to non users and our Suppliers are not Users.
But you can make a Report of all Suppliers who have Open Products not received and by using a special form for this purpose include an embedded report of all Open Products.
Then you can Make a subscription report to come to you daily.
Then on the report you can make a URL formula button which will update a date/time field called [date/time emailed to Supplier] with the current date and refresh the report. The report will have a filer on it to not include Supliers emailed today.
So each day or as often as you choose to send the report, you or someone will mindlessly click a button on a record and trigger an email to Supplier based on a Open Notification and the Notification will be set to use a specific form for this purpose.
Once you get that working, it it becomes annoying to push the button so many time, you can contact me or another QSP who can install a script so that you only have to push the button once, to trigger separate email Notifications to all Suppliers on that report.
If you want to completely Automate that with no button pushes, I can hook you up with Juiced who can, for a monthly fee, completely automate this with no button pushes.
I can help you with the URL formula button if you like.
