Global Delivery Model – What is it?

Technically, you can't, since SMTP is designed in a way that you can't know for sure if the email was delivered.

If you're sending legitimate emails and their potential readers are willing to help you (for example some critical notifications sent to the employees of your company), then "Request a delivery receipt" option comes to mind.

Of course, if one of the employees don't want to send the receipts back, you'll never know if the emails were delivered or not. The same comes for people who explicitly set their email client to discard any delivery receipt requests.

If you want to be sure the messages are "technically delivered" to the users, then consider another way, like showing those messages on your corporate website and log the access of the users.

Last but not least, even if a message is displayed to a user, it doesn't mean the user read it.

Zero-downtime releases using Azure App Service slots and a single database shared by Staging and Production are possible - but you need to make sure that all database changes are backwards compatible, such that the current and new versions of the web app can run simultaneously in the Staging and production slots.

Some rules that ensure this works:

• Any new database columns should be nullable or have default values
• Renaming columns is not permitted
• Dropping columns is not permitted

When you do need to make destructive changes, such as renaming or dropping columns, you need 2 releases to do this:

1. The new version of the web app should be released, which removes the dependency on the renamed/dropped columns
2. An additional release is made that performs the destructive changes

While this sounds a bit complicated, in practice you likely won't be making destructive changes very often.