Originally, the Simple Mail Transfer Protocol (SMTP) used port 25. Today, SMTP should instead use port 587 — this is the port for encrypted email transmissions using SMTP Secure (SMTPS). Port 465 is also used sometimes for SMTPS. However, this is an outdated implementation and port 587 should be used if possible.

In case that's helpfull to anyone... :
You can set this in your panel.ini :
[mail]
clientConfig.incomingServer="mail.<domain>"
clientConfig.outgoingServer="mail.<domain>"

It will setup mail.domain.tld for the autodiscover/autoconfig, for every domain.

You have to empty the custom field in “Tools & Settings” > “Mail Server Settings”, and tick the box "Reconfigure autodiscover DNS records" for the for the changes to take effect

What does PLESK do with that specified domain name? Can PLESK staff be so kind and provide some documentation?

Will it (only) provide script (which returns XML content) in the local subscription that contains this domain?

Will it (as well) return that domain as the SMTP's/IMAP's/POP3's name as part of the XML content?

From my POV, both are required in order to make the feature usable "out of the box", independetly from any individual configuration in a subscription, i.e. without subscribers' need for registering a certificate (accepting a CA's terms etc) + doing other operations in plesk's panel.

I agree this is not an adequate solution by any means. We need this solution to be a domain- or subscription-level solution, and we need to be able to customize the type of mail server listed as POP or IMAP for the output. Custom Port numbers would be nice too. C'mon guys just a few more user-defined variables here!

The solution is not a per domain feature :(

+1 on this feature. We need granular control over what settings the mail client picks up. This would also solve the problem of the hostname being the blank domain name, where the domain's emails are hosted on Plesk but the website is over at Squarespace, or whatever. There's a reason why configuring DNS records is important for each domain and Plesk should take advantage of this.

Please consider adding this feature.

+1
it would be useful the possibility to change the wrong/default values for the ports 993-465-995 and authentication SSL in the xml file generated automatically for every domain (e.g. with 143-587-110 and authentication STARTTLS):
https://<domain>/mail/config-v1.1.xml?emailaddress=<email>

Now autodiscover is meaningless because it provides wrong values if you don't use the default settings.

Custom hostname per mail domains would be good.
pop3 or imap service offering per mail domains would be also welcome

Seriously need to be able to set all autodiscover variants to POP3 instead of IMAP, globally.

In it's current state Autodiscover in Plesk Obsidian is completely useless; does NOT even work with e.g. Outlook 2016. Worthless...

Another setting we need control of is the choice to promote POP or IMAP as the main (or only) autodiscover setting. We need to be able to set custom hostnames, AND preference between POP and IMAP via a GUI setting. Currently I'm having to modify the files in /usr/local/psa/admin/htdocs/mailconfig/ to make my clients use "mail.domain.com" server name and POP server settings — and it is working! I know this can be done easily, because I'm manually doing it every day with a crontab script. Please make it stick. Thank you.

Compelling when mail.customerdomain.tld is used instead of (mail.)serveralias.tld