Add a setting to disable mail forwarding to certain domains in Panel for global configuration so that on user side wont be allowed to put the certain domains in the Forwarding Email in the Plesk Panel. Thank you.

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

Ability to use MySQL as an extension to Dovecot
Business case: using MySQL database for centralized authentication to email accounts.

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

An option to customize outgoing SMTP port.
Both for SMTP relay and direct SMTP.
Currently there's only a temporary workaround for Google Cloud VMs with Plesk.
This configuration might be overwritten by an update:
https://support.plesk.com/hc/en-us/articles/115004060494

When there is a SmarterMail service running on the same server with Plesk, it would be great to have an option to create an account in Plesk with the same domain and attach the SmarterMail content.

Add an ability to register webmail in the following format: http://mail.<domain>, so the customer can open it via http://mail.example.com

We use the following configuration on Plesk for Windows: in MailEnable postoffices folder, domains' folders are junctions to folders inside subscriptions' web folder (e.g. C:\inetpub\vhosts\example.com\email). In Plesk Onyx with such setup, statistics were calculated successfully but in Obsidian, it stopped counting the size of junctions, so the mail statistics is counted as 0.
This setup is important for us, so please return the support for domains' mail folders as junctions.

It is no longer possible to create mail accounts without a password in Plesk Obsidian. However it is required to create such mail addresses for Forwarding as example.

Add an ability to enable auto-reply only for a particular sender, so the bounce-back message is sent only to this sender

Implement outgoing email limits by IP

There are trusted mail servers with incorrect/broken DKIM.
It's needed to exclude such mail servers from DKIM checker. Tools & Settings > Mail Server > White List doesn't allow to exclude mail servers from DKIM/DMARC/SPF check.

Configure the postfix bounce notification email, to be notified whenever Postfix is unable to deliver a message.

Add to Plesk Email Security setting that shows weekly difference in mail statistics. For example, show "+55 emails sent to spam last week"

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

Sometimes, when emails are manually migrated or restored from a manual backup, it is required to update mailboxes' indexes so migrated/restored emails are available via IMAP.
Such functionality could be added to the utility "plesk repair mail" so it is possible to update indexes in automated way.