email

Key features:

• Kint (enable kint submodule, for pretty variable printing, way to view properties and methods)
• DevelMailLog (redirect all mail to text files instead, specify location directory, specify filenames using tokens for recipient, subject, timestamp) - DevelMailLog requires that you also install the MailSystem module to activate it
• Config Editor and State Editor (enable via /admin/config/development/devel/toolbar)

Send mail to a remote SMTP server (e.g. a transactional email provider like Postmark).  

You should put your authentication details in settings.php, rather than files you commit to the repo, for security.  

To get this to work - it was sending tests but nothing else - it seemed I needed to switch to a commit on the dev branch:

"drupal/smtp": "dev-1.x#3d354b3911409c9b11716bf2104498fb431eea72"

(note to self: see SM notes) 
 

Store all contact form messages in the database (as an entity), rather than just emailing them.

Integrates with views, if you want a view of messages.

Messages are accessible (can be edited or deleted) at /admin/structure/contact/messages.

(May be useful considering From: address SPF/DMARC problem with contact forms, i.e. there may be cases where some emails aren't delivered.)