It seems, some of the people do not understand what we exactly need this feature for. At least from my side I would like to take the opportunity in order to give you a better understanding.

Yes, currently it is is possible, secure the mailserver with a certificate. However, this would mean, that every user has to use my.servername.abc or mail.coolprovider.xyz

At least we have multiple plesk servers and when migrating users between the machines, we do not want to force people changing their configuration. In many environments changing the email client settings is not that easy as it seems, f.e. in hospitals. Some customers even have their own exchaneg server with a small tool fetching the mails.

So it would be a requirement to find a solution using let's encrypt for securing mail.domainname.xyz - however for all domains on the plesk server.

Yes, it might be, that postfix does not support this feature because of SNI. But some people in forums are also discussing, that a mailserver proxy providing the certificate, and then forwarding the request in plain to the local postfix on another port could work.

valid feature request, I am interested in using Let's encrypt to secure IMAP/POP/SMTP

@Plesk Staff: fraud attempt?!? where do you see fraud? how do you explain fraud attempt here?

little less conversation, little more action as Elvis would say

In my opinion this is a valid feature request. I had hosts screwing up the certificate renewals for email services. Let's encrypt would be a perfect fit for that.

@Plesk Staff: Are you serious about the fraud attempt? What does this even have to do with the feature request?

Lets get this done!

spend less time creating extensions (that cost to use) and lets get some of these wanted feature requests implemented into the plesk core (with having to pay more via an extension).

Reply to Marco Marsala´s comment on April 20, 2018 11:09:
This works only with hosting service enabled and does not work for mail-only Servers, besides it would be a huge effort to do this manually.

@PleskHelps, May 18th via Twitter:
"Mail services used by Plesk do not provide that functionality, so there is going to be no such feature in Let's Encrypt as well."

one more vote from my side. So needed to avoid this messages.

Please implement this as soon as possible

At least until LE support multidomain certificates.

And I know most MTAs support multiple SSL certificates! So, itf mail server is secured with LE, it is just matter of generating a new LE certificate every time a domain is created, and adding such certificate to the mail server configuration. Certificate should be generated for domain: example.com and their popular mail subdomains like: mail.example.com, imap.example.com, smtp.example.com)

Actually you can automatically secure with Let's Encrypt example.com, www.example.com and webmail.example.com. Why don't add mail.example.com, imap.example.com, smtp.example.com, that are tried as default from most e-mail clients and cloud mail services when you insert an email address?

They're just 5 popular subdomains (the number is matching current LE restrictions).