How to automatically issue Let's Encrypt certificate for newly created domains?

Question

How to automatically issue Let's Encrypt certificate for newly created domains?

Answer

Enable Keep websites secured with free SSL Certificate in Plesk > Service Plans > click on desired service plan > Additional Services > Let's Encrypt - Keep websites secured with free SSL Certificate > Update & Sync. 
All newly created and existing domains will be secured by Let's Encrypt within a hour. 

OR

In order to issue a  certificate with Let's Encrypt for every newly created domain create two Event Handlers at Tools&Settings > Event Manager with the following parameters:

PLESK_INFO: Event = "Default domain (the first domain added to a subscription) created"
Priority = 75
User = Plesk Administrator
Command = plesk bin extension --exec letsencrypt cli.php -d <NEW_DOMAIN_NAME> -m mailbox@example.com

PLESK_INFO: Event = "Domain created"
Priority = 75
User = Plesk Administrator
Command = plesk bin extension --exec letsencrypt cli.php -d <NEW_DOMAIN_NAME> -m mailbox@example.com

The only limitation is that valid email required to issue a certificate. However, event of domain creation does not support email variety.

So, to automate the whole process (with no need to enter an email of each client) just enter email of Plesk administrator or any other one which all certificates will be assign to instead of mailbox@example.com in the example above.

Additional information:

If Let's Encrypt is enabled in Additional Services of a service plan, will existing domains be secured?