By default use an existing email created by default as a return path . Return path should be configured in mail tab instead of solution from here:
https://support.plesk.com/hc/en-us/articles/115000419013-What-is-the-return-path-sender-in-PHP-mail-scripts-and-how-to-change-it-

Some mails could not be received due to the fact the Postfix 2.8 and higher in Plesk uses only TLS encryption, when senders use other encryption methods. Manually updating main.cf directly on the server (as discribed in https://plesk.zendesk.com/hc/en-us/articles/213386889) is not always an option since the main Postfix configuration file may be overwritten by any Plesk update. In order to avoid potential issues with non-delivered mails it is required to make SSL/TLS encryption on port 587 optional, not mandatory.

It's required to send Plesk notifications using external Mail server at the same time keep local mail server(postfix) working for domains.

Allow email address, local part to have characters such as $ as per RFC3696 which allows ! # $ % & ‘ * + – / = ? ^ _ ` . { | } ~

My problem is that I have moved my hosting package from eXtend to Plesk, and suddenly I have a bunch of email accounts I cannot re-create.

I would be a good Idea to be able to change webmail URL via Plesk, not using workaround https://support.plesk.com/hc/en-us/articles/213947325-How-to-set-up-an-access-to-webmail-over-mail-example-com

if smartermail is local install you can create a SSL for webmail. This doesn't work with remote smartermail.

I would like plesk to introduce this so some kind of agent is running on the server so Plesk can communicate with IIS on the remote web server to copy SSLs and bindings.

I like it to create eMail aliases in many situation. It would be great if it is possible to move Mails to a specific directory.

Could you please add support for dovecots subaddressing feature?

To be able to sort the email list by alphabetical order and able to reach an email by typing the first letter with effect to point at the first email with this first letter typed.

Device Authentication for email, this is a must have feature

I need to save the email attachments of both received and sent mail by saving them in an ftp folder of my account, so I have them already available to catalog them
thankyou

Restrict what attachments are to be filtered by Mail server. Example
All Domain > Block Extension > exe,jar,rar,gzip

Instead of fail2ban for roundcube, use CAPTCHA so people are not getting randomly banned.

Currently the only way to get the DKIM key is to decode the private key from the shell when using an external DNS service, however it would be nice if the public key is just being displayed in the web interface so the user can see it and add it to the external DNS.

Pain staking issues as soon as setting up mail is not working like normal. How nice would config files be! For differten platforms.

It is important to know what transfer rate each email account has per month to detect abuses in the use of the email and avoid exceeding the established limit

Create a new option for mail to nonexistant mail in a domain, an option that allow discard this kind of mails. Actual options can cause unlimited bouncing if sender domain doesn't exist.