It would be greate to have a permission in service plan which allows customers only to restore backups with out possibility to downlaod them
That will give an option to upsell hosting plans with extra option

Currently, it is only possible to limit mailbox creation for a subscription, but mail accounts could be further created, exceeding this limit, which could confuse end users.
Please add ability to limit the creation of mail accounts for subscription.

Create a feature that enables switch off background services on Plesk like Extension catalog, Application (APS) catalog, KA service to trying to communicate with external Plesk's service servers on the internet.
It will be usefull on Plesk servers that will be placed on internal/intranet networks were access to the internet is not possible, since requests to external services makes Plesk UI slow as the connection to external services fails.

Mail forwarding, when sent externally, can cause IP reputation issues due to forwarded spam.
When users setup an email account via Plesk panel, they are given the option to "Switch on mail forwarding". It would be nice to either disable or hide this option from plesk panel. If
that's not possible, then only offer users to forward email locally instead of forwarding to external email accounts

Add Native Plesk Email Notifications for following Plesk events:
Panel User Login
Panel User Login Attempt Failed

It can be associated with time stamp, URL, IP, event name, login name.

For now, this functionality can only be achieved with the Plesk Event Manager and custom mailing scripts.

when sending alerts about high load of server, i think it would be a Good idea to receive some kind of snapshot of processes list, maybe not the full list but at least first 10 or 20 heavier processes

In the meantime you receive email and go to panel to see what is happening. things goes back to normal

Allow merging multiple email notifications into one, this to avoid bombarding for example new Customers with 2 to 4 mails instead of 1.

At the moment variables like {{ Domain }} cannot be used inside the "Notification of the customer creation" mail for example

So it is not needed to have a domain resolving to any DNS in order to access the webmail.

Permission "Hard disk quota assignment" does not allow to manage "Hard quota on disk space" for customer, but it doesn't hide "Hard quota on disk space" notice for customer in "Web Hosting Access"
It's required to hide this notice for customer.

As what I can see, Im only able to control the SPAM filtering per user account address, there should be a main option where I can set all the email accounts SPAM settings like the sensibility level, and whitelisting/blacklisting.

To secure a Plesk mail server with different SSL certificates (SNI enabled), it requires to have dovecot:
https://support.plesk.com/hc/en-us/articles/115001446174

There is no such feature for courier imap server, please integrate it as well.

I would like to automate domain customer's FTP access to a domain.

So I want a user to be automatically notified about their newly created FTP access when creating it in Plesk UI.
Writing an email with credentials for every customer is ineffective and time-consuming

We are using Plesk with remote smartermail server. When creating a mailing list in Plesk, only the Moderator can send "Post" to that mailing list by default. We manually have to go into smartermail as domain admin and change the the Posting to "Anyone" which should be the default settings. See for details https://help.smartertools.com/SmarterMail/v2/Default.aspx?qq=%2FSmarterMail%2Fv2%2FTopics%2FDomainAdmin%2FLists%2FGeneralSettings.aspx
We would like to have this option available in Plesk.

This would allow mail users to perform a password reset on their own. Currently this is not possible, because the email with the reset link would be sent to the own address. (To which the users usually have no more access without a password)

For reasons of data protection, it would make sense that the email passwords can be reset independently and not by the provider.

I'd be great if you could configure that Plesk looks in Active Directory for users of a specified group and fetch their email adresses to create these

Postfix does not send bounce notifications when a user's mailbox is full. It would be useful to disable these notifications for qmail as well.

It would be great to have an ability a report of the total number of emails sent by each user per month or other timeframe

It is currently possible to change webmail attachments sizes only via config files on the server as explained in the following article:
https://support.plesk.com/hc/en-us/articles/4404961923474
Would be convenient to change webmail attachments sizes in the Plesk interface.

There should be an option to forward mail without letting the customer know it is enabled (to the extent permitted by the law).

Currently, it is possible to hide all mail settings from a service plan or subscription. More granular control to hide mail forwarding only, or an option to enable it separate from the customer's own forwarding settings, would help monitor malicious content.