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.

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.

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.

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.

Add the ability to download/upload a list of the domains from Whitelist of Blacklist (Tools&Settings > Mail tab) as a text file so it is possible to add all the required domains at once.
The following Uservoices matching this feature were already created serveral times:
https://plesk.uservoice.com/forums/184549-feature-suggestions/suggestions/15998113-server-wide-e-mail-settings-blacklist
https://plesk.uservoice.com/forums/184549-feature-suggestions/suggestions/17805055-download-and-upload-for-the-email-blacklist-in-ord
https://plesk.uservoice.com/forums/184549-feature-suggestions/suggestions/6345455-mail-server-settings-bulk-emails

Not sure how can this be implemented but mailboxes getting full from messages(spam) that gmail does not download

It would be nice if there is a way to auto clean undownloaded messages after a while

Allow the Pleask user to specify a mailbox with no (zero) capacity for the purpose of managing email from a 3rd party such as Gmail. This would allow email to be forwarded to Gmail without the exceeded capacity error but also allow Gmail to send mail through the mail domain. Currently this needs to be modified by admin and it's hard to explain each time to the admin.

The use case. Messages deffered to Yahoo when many messages sent:
421 4.7.0 [TSS04] Messages from IP temporarily deferred due to user complaints

Is it possible to add limit outgoing messages to specific service, for example:

Sent no more than 100 mail to Yahoo per hour

If you have configured additional delimiters in postfix (/etc/postfix/main.cf) it is not possible to successfully deliver a mail to a mailing list - if that mailing list address contains also one of the symbols configured as delimiter.

The solution is very simple and could be a very generic change in plesk standard config:

In /etc/postfix/master.cf just change the config string for mailman in the end of line from ${nexthop} ${user} ${recipient}
to:
${nexthop} ${mailbox}
This will parse all necessary parameters before the @.

Taken from: http://www.postfix.org/pipe.8.html

Additional Administrator Accounts would like to stop receiving certain emails generated by Plesk. Would like to be able to control these.

Recent example of one not needed by one additional admin
"Could not issue/renew Let`s Encrypt certificates for Administrator"

Add to email address mailbox configuration - after mailbox size.

I would like to see the possibility to enable periods ('.') in email folders. Reason for that is that there are some webshops around here using the period as full store name and I would like to keep those emails in a separate folder.

As Google or Microsoft mail service, it can be great if when a user of a mailbox the name of the sender is overwritten by plesk.

Like this, we can provide a better and secur mail server. Mainly for developper or webmail.

Exemple :
I use the mailbox JD@domain.com and on few mailserver (as google), the sender will be JD if we use webmail, php script, etc. But if when we create the mailbox, and we assign the name "John Doe" to this mailbox, the sender will be John Doe.

Thanks for your help

Hello,

It would be amazing to be possible to create a distribution list via Plesk Premium email without creating a mailbox and forward the emails.

eg. create a example@example.com without a mailbox and forward to a group RH or Sales.

Hi!
It would be great if the autoresponder may switch on for a whole domain

For our customers I need to be able to use "smith.domain.com" as their Email Username, as opposed to their email address

extend the webmail settings screen like the php settings.
show the amount and which domain is using which webmail client and allow changes to it.
now after the horde desaster it would be way easier to identify domains using it and changing that.