Nice in theory, but just when I think I have it figured out something changes and the script quits working. Specifically with 3rd-party hosting like NearlyFreeSpeech, not my own, but still a PITA.
I have a running system with Let's Encrypt certificates for webserver (HTTPS) as well as mail server (SMTPS, IMAPS, POP3S), based on nginx, exim4 and dovecot, using certbot.
Setting up Let's Encrypt literally consists of just 3 steps:
1. In the webserver for all domains on HTTP, add alias /.well-known/acme-challenge to /var/www/letsencrypt/.well-known/acme-challenge
2. Run "certbot certonly" once for every domain
3. Add cronjob for "certbot renew" with a post-hook that restarts your webserver and mailservers.
Well, to be honest, there is one more step, but that one is specific to my own setup, and also just a one-time effort:
3a. Add a post-hook command that fixes a permission issue with Debian-exim. Note that this is only needed if you want to use the certificates for SMTPS and use exim under Debian.
If you add a new domain later on, this is just a single step, no need to touch the cronjob:
1. Run "certbot certonly" once for that domain
So yes! Once you have the setup running, setting up a new SSL/TLS domain is actually easier with Let's Encrypt than with any other CA.
(Of course, you'll also have to add the domain to your webserver configuration, but that's always needed, whether you use Let's Encrypt or not.)