Would be good to be able to manage SMTPUFT8 option over Plesk so that it is not reverted after Plesk Updates and also to remove the need to manage this option over the Postfix config directly.

More information:
https://talk.plesk.com/threads/smtputf8-is-required-but-was-not-offered-by-host.351377/
http://www.postfix.org/SMTPUTF8_README.html

By default, the Mail Audodiscover function does not set the Root folder path to "INBOX" in Outlook, which results in an odd directory structure:

Inbox

 Drafts

 Sent

 Trash

 Spam

Outbox

Please provide a way to configure this without having to manually edit the mail server configuration files.

The actual MailQueue status is useless, becaus the "status" of the email isnt viewed. This contains the important information for mails with problems.... Please expand it with the status, like it is done win Webim for example

No suggestion, but a critical, urgent, overdue feature request, as described in many "suggestions" since years:
Secure
mail.customerdomain.tld
webmail.customerdomain.tld
with Let´s Encrypt certificate without having to set the DNS A Record for
customerdomain.tld
to the mailserver IP.
And withouth having WAF disabled (SSL It 1.20 is being blocked bei Comodo (free) and Atomic (free) rules, other not tested yet).

Add an option to set a delay to the Postfix auto-reply. Currently, it sents instantly.

Add mail autodiscover functionality for iOS/OS & android mail clients please.

An option to reset email password using Forgot Password? on the Roundcube or Horde login screens.

Having a built-in REST API for IMAP, either similar to or compatible with the Gmail API would be amazing, especially if you could limit user rights in Plesk so that you could have domain specific access, or read-only access etc. The imapapi linked to nodemailer is a huge step forward but integration with Plesk would be ideal since security is paramount for an API that can access mail. Obviously this is a long-term request.

Plesk already provided with Remote Smartermail same like

if Plesk provides Remote Mailenable or any other email servers. which will be easy to manage mail server remotely instead of the same server to reduce the emails via scripts and blacklist issues.

At this time, access to spamfilter settings for a mailbox are only possible for admins and website owners. Pls make it possible for logged in mailbox users to access and edit there own spamfilter settings.
It's very important, because on website's with many mailboxes, the admin often cannot support all users in setting up there spam settings.

Please make Plesk Premium Email available as a PWA (Progressive web apps).

So that we could "install" Roundcube as a PWA on our Phones.

Seeing as the current implementation does not work with Outlook (and a lot of people use Outlook), it would make sense to remove the digest-md5 option from dovecot and postfix configs. These options keep coming back on a Plesk update so it would better to just remove them completely.

https://support.plesk.com/hc/en-us/articles/115001001933-Cannot-set-up-Plesk-mail-IMAP-account-in-Outlook-SASL-DIGEST-MD5-authentication-failed-authentication-failure
https://support.plesk.com/hc/en-us/articles/213917625-Outlook-fails-to-send-an-email-SASL-authentication-failure-On-Plesk-for-Linux

Since Kolab Syncroton does not enable sync on newly created folders, it should be enabled manually.

They would need to select the ActiveSync device ID, click to enable the synchronization of the folder and save the changes.

While it was nice if there will be an ability to do so automatically.

Add the count of messages in the postfix mailq to Advanced Monitoring and Grafana. Then we have the option to get alerts if mailq goes up, in case of spam events!

In case some mailboxes send spam on behalf of my customers, I would like to have an ability to block their mailbox from sending emails to particular domain or mailbox that exists externally

I want to be able to customize master.cf. But, currently, any customizations to master.cf get overwritten.

Currently, Plesk has an option to enable mail forwarding for particular mailboxes of the domain; and it is also possible to forward all incoming domain's mail to a single mailbox.

Please allow activation of mail forwarding to another domain for all existing mailboxes at once.

To allow one click mail forwarding as follows:
mail for user1@domain.com redirected to user1@domain.net,
mail for user2@domain.com redirected to user2@domain.net, etc.

Example:
Malware has created a lot of spam that was sent from the domain example.com and the mail queue is full.
I would like to have the option to find all the emails from that domain in the mail queue and remove them with one click instead of obtaining the mailqueueIDs and trying to push them to "postsuper -d -".

To make it simple, it's a filter (e.g. sender contains example.com) + option to remove.