Ability to change settings in the mail autodiscover - for example, to set the mail server that will be set in the mail client.

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 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!

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.

Allow changing the percentage when the mail quota warning is sent, in small sized mailboxes the 95% could be almost to late.
So it would be good to have an option to adjust it for example to 85% or other values.

I've installed 1.4 manually and it works without problems.

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

It would be nice to have dovecot replication https://wiki.dovecot.org/Replication

According to https://support.plesk.com/hc/en-us/articles/115000786914-How-to-enable-SpamAssassin-spam-check-for-forwarded-emails-on-Windows when the option "Apply individual settings to spam filtering" is enabled, filtering of forwarded emails is not performed and additional steps are required.

Please, make it so that no additional steps would be required.

Please add functionality to access webmail from Plesk interface without using a password.
The same functionality is enabled in cPanel. Please see section "Access webmail from the cPanel interface" of documentation:
https://documentation.cpanel.net/display/CKB/How+to+Log+in+to+Your+Server+or+Account#HowtoLogintoYourServerorAccount-AccessWebmaildirectly

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!

When installing Plesk with MailEnable, by default Plesk removes MailEnable logfiles every 24 hours.

According to this KB (https://support.plesk.com/hc/en-us/articles/115001102353), this functionality is made in purpose to optimize mail statistics, but this is not acceptable.

Additionally, you are offering the possibility to apply this workaround (https://support.plesk.com/hc/en-us/articles/213397889), but this workaround is not valid for us because we don't want to customize the FTP and HTTP logs location and we have the log files in different disk volumes.

Please, provide the possibility to configure the log rotation settings for MailEnable respecting our hosting company needs.

An option to choose IP for outgoing mail on domain basis.

For now, only below options available:
- all the domains send from particular IP
- each domain uses its IP address

This feature is for use case when one or several domains can send through one IP address, and the others through another one.

It should be managed independently of web hosting IP address.

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.

It would be convenient to be able to enter 2 contact email addresses. One for general purposes and another for technical support purposes. My brother manages the content of his site which I build for him in Wordpress. I manage the updates and all other (too technical for him) issues. Currently he gets all mails from ImCloud, it would be nice if I would get update warnings etc directly on my own email address.

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

Currently all mailbox passwords(MailEnable) are stored in AUTH.TAB in plain text that is not secure.
MailEnable has an option to enable password encryption in AUTH.TAB

As a Plesk administrator, I would like to set the sender email addres for PHP scripts.

The below article isn't applicable when using e.g. WordPress.

https://support.plesk.com/hc/en-us/articles/115002799114-How-to-send-mail-via-PHP-script-using-a-mailbox-located-on-another-server

p.s.: the article created based on comments to this article: https://support.plesk.com/hc/en-us/articles/213931945-Mail-to-external-mail-service-is-delivered-locally