Surface errors / error messages in UI

[cahdeemer]

Description

I would like to see errors or error messages surfaced in the Newsletter Builder UI so that when a newsletter fails to send, there is a message in the UI.

Along the same lines, I would like required fields to be marked as required (example: From Name) so that when a user understands that the newsletter will not send when that field is not populated.

Use Case

We had an issue where a Lede publisher didn't receive a test email. We discovered that the email didn't even make its way to SendGrid. The publisher hadn't set up a verified sender in SendGrid so the From Name dropdown in NB wasn't populated. There wasn't an indication in Newsletter Builder that this field was required and there wasn't an indication in NB that the email failed.

Notes

• It would be useful to keep track of error messages in a way that could be surfaced to users even if the error happens asynchronously. For example, if a newsletter is scheduled to publish and that action is triggered by cron, the user won't see any synchronous error messages, and would need to see the error when viewing the WordPress admin at a later date (for example, we could save the error message to usermeta for the user that created the newsletter, and dismissing the error could clear it from usermeta, as one suggestion).
• There is already a status panel for each newsletter, and error messages could be attached to newsletters and surfaced in the status panel. This could also be a partial solution to the bullet point above, where maybe what gets set in usermeta is the ID of a newsletter that had an error, and the error itself could live with the newsletter's data.