Most of the situations where WordPress sends an outgoing email can be classified as a notification. X just happened on your website and you should be aware of it.
Back when WordPress was a youngster, the only way to reliably notify a user was via email. In 2016 we have many more options, including push notifications to mobile platforms, desktop notifications to browsers, messages to chat apps, endless services via webhooks, SMS messages, or even notifications in the WordPress admin area. The list goes on. For many users, email is no longer the optimal delivery mechanism for ephemeral notifications.
To that end, let’s think about replacing
wp_mail() with a modern API that allows developers to route notifications to services other than email, allow them to better modify notifications and the way in which they’re formatted, and allow them to do so without stepping on each others’ toes.
The current lack of a notifications API (or even an email sending API) can be easily summed up:
Problem: Plugin A wants to provide HTML emails, and Plugin B wants to send emails via an email delivery service such as Mandrill. Plugin C wants to disregard emails and send Slack notifications. It’s very difficult for these to co-exist.
There are only two types of destination for a notification in WordPress. Most notifications are actually notifications to a user account that get delivered via email because it’s the only contact information available for every user account. The remaining notifications are explicitly notifications to an email address rather than a user account (or not yet attached to a user account), such as when a user signs up for a blog and needs to click a confirmation link before their user account gets created.
With this in mind, you might be able to imagine a notification class in WordPress core that defaults to delivering notifications via email, but which can be extended by a plugin on a per-user and per-notification basis to deliver notifications via any of the means listed above. WordPress core would support delivery via email and provide the API that allows plugins to implement delivery via other means.
With a well-designed API, multiple plugins can co-exist in order to deliver different notifications via different mechanisms, format email notifications as HTML, easily disable notifications, change the delivery mechanism for email notifications, or provide a UI for users to manage their notification preferences and destinations.
Planning a Notifications API
I’d like to begin work on a feature project with the intent of designing and implementing such an API. I’d like to get input from authors of existing plugins that provide functionality such as delivering notifications via a service other than email, that override the default email delivery mechanism, or that implement extra notifications (such as e-commerce sale notifications), in order that the API can be backwards compatible and that we can get some plugin implementations built during the API’s development.
I already have some technical ideas regarding how the API might look, but I’m conscious that such an API needs to be well-designed before anyone jumps into writing code. Maybe we can even try some test-driven development? Who knows.
In addition, consultation and involvement with the team that are working on the two-factor authentication feature project is important as it implements several delivery mechanisms for 2FA codes that could potentially be made simpler with a notifications API.
Feedback is most welcome in the comments. Would you like to help out? Yes? Great. Let’s plan a date and time for a meeting in Slack and go from there.
Finally, a reminder that feature projects are not tied to a specific release of WordPress. This won’t make 4.7. It would be great if it was mature enough for 4.8, but we won’t be aiming for a particular release just yet.