create a specific mailbox on a domain which customer has access where he is unable to delete the email address, change it's passwords, disable it, etc.

According to Postfix documentation, multiple Postfix instances are supported. Would like to have such support implemented in Plesk
http://www.postfix.org/MULTI_INSTANCE_README.html

Hello,

On plesk you can only configure the Let's encrypt SSL on the webmail not on Smartermail.

It would be a great addition to add the same support also for Smartermail

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 email specified at Scheduled backup notification it sent on behalf of user and failed due to SPF check

For example, if you set email for backup notification as test@example.com the email will be sent FROM test@example.com. And if it does not exist on server it may fail during SPF checl

It is expected that email sent FROM administrative email.

Add an option to the Mail Addresses page to expand all the forwarding emails. For example, rather than saying "(and 4 more)" list all 5 forwarding email addresses, not just the first one for each email address on the display.

Add an ability change the mailbox quota threshold and send the mailbox quota warnings to server administrator or to a specified mailbox.

You should add a simple option to specify mail server hostname when autodiscover is enabled on domain level...

example:
main.domain -> Web
mail.main.domain ->Mail server (this one should be in autodiscover xml response for incoming/outgoing hostname )

Is it currently possible to set only one mailbox to forward the mail for non-existent users in Domains > example.com > Mail > Mail Settings > Forward to address.
Please allow to add more than one email address for this setting.

By current design of Plesk SSL certificates selected to secure webmail in Plesk doesn't secure IceWarp webmail URL.

Consider adding this functionality.

It'd be good to be able to migrate Contact & Calendar from cPanel to Plesk.

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

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.

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.

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

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

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.