How to fix E-Mail problems in WordPress and WooCommerce

A frequent issue in WordPress or WooCommerce: Email do not get sent. Here is a suggested path to resolve this.
Step 1: Install a log to see if mails get triggered
The first thing you want to do when dealing with this is make sure, that there is email activity to begin with. Here are two plugin that can help you:

Install one of them, then repeat the action that triggers the mail (register for a new account, purchase a product in your shop) and take a look at the log.

How to fix WooCommerce Subscriptions crashing site – get_editable_roles error

Having trouble activating WooCommerce Subscriptions on your site because activation of the extension crashes your site completely? Look at your error message (if you have none, activate WordPress debug mode) If your error messages includes a failed call for get_editable_roles
then we got you covered.
Download this patched file (fixed by Gabor Javorszky, thanks!), courtesy of Prospress and replace your includes/admin/class-wc-subscriptions-admin.php.
This should solve the issue.
Download WC Subscriptions patched file