Questions about Let's Encrypt SSL


1. Ho many maximum sub-domains can use this SSL, is there any quantity for per-domain?

There is not limit on how many domains can use a certificate. However, you can only generate 50 certificates per domain per 7 days according to Let's Encrypt
The subdomains from the same domain zone like and have the same rate limit. Thus, when the first 50 domains of get a certificate, the rest need to wait for a week. 


2. Is there anyway can use this SSL for mail.DomainName it's also consider as sub-domain.

So far securing the mail server for multiple domain names (known as SNI) is a feature that it is not implemented in Plesk because the mail server does not support it: Is there SNI support for SMTP/IMAP/POP3? However, you can secure the mail server by following this article:

In regards to your other request, it is possible to access emails via instead of Please refer to the following article: How to set up an access to webmail over