Currently, there are three buttons in the mail queue interface.
Refresh, Remove, Clear

These are fine when there is Spam in the mail queue but for normal emails, it would be nice to have an additional "Requeue" button.

Now, when I spot an email that shouldn´t be deferred I have to log in over SSH and execute: /usr/sbin/postsuper -r ALL to requeue them.

Just like the "Remove" button works for selected emails the "Requeue" button would work for requeueing selected emails.

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

That the administrator is able to set a different sender of the forwarded emails.

It would be useful to be able to add domains to IgnoreMailFrom rule for DMARC check from Plesk interface.

Hello,

At the moment mail server shipped with Plesk is not able to store or handle emails compressed by Gzip on the file system.

Please add functionality to support compresses emails or option to enable email compression.

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

Add delete/reject option for addresses and or domains in the blacklist. If I've blacklisted a domain, chances are that I don't want anything from that source.

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"

It would be a good idea to be able to set mail filtering for emails with specific Subjects in Plesk Email Security extension.

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

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

Add the function in Plesk to be able to modify the return path on the autoresponder of MailEnable

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).

Mail authentication brute force attacks generate additional traffic.
It is counted as a part of POP3/IMAP traffic statistics in Plesk for Windows.
Please add functionality to recognize and ignore such normal traffic so that it does not forge POP3/IMAP statistics.

Add domain reputation based spam protection lookup such as the feed from dbl.dq.spamhaus.net, in addition to the existing IP DNSBL.

If I import mails I enter username and password. These are stored so I can synchronize at any time. But when I wish to delete the credentials, there is no option for it! Username and password are store in clear text somewhere on my provider's server and they cannot be deleted. That is a security failure!