How do I get the Settings System email Address?

In craft 3 it appears you can access it by doing the following:

{{ craft.systemSettings.email.fromEmail }}

The craft.systemSettings variable was been deprecated as of Craft 3.1.0, and removed in Craft 4.0.

Here's how to get the system email address in Craft 3.1.0+:

{{ craft.app.projectConfig.get('email').fromEmail }} 

Important: If your system email is set to an environment variable (e.g. like $SYSTEM_EMAIL_ADDRESS), you can use the parseEnv() Twig function to render it:

{{ parseEnv(craft.app.projectConfig.get('email').fromEmail) }} 

Other email settings such as replyToEmail and fromName are also available via craft.app.projectConfig.get('email'), and can be access and used in the same way as the fromEmail.

Alternatively, email settings can be accessed via the App helper class, although it is generally discouraged to instantiate the App helper class from Twig:

{% set appHelper = create('craft\\helpers\\App') %} {{ appHelper.mailSettings.fromEmail }} 

Or in PHP:

$fromEmail = App::mailSettings()->fromEmail;