Issue SMTP port 587 with SSL not working

[ChrisCP]

Hey to all.
I figured out that sending mails via SMTP port 587 with SSL is not working. On port 587 only STARTTLS works on clients like thunderbird or mail programs on smartphones...
On port 465 SSL is working fine for all clients. I use latest version of Plesk and postfix for smtp server.
How can i make it work to send mails via port 587 and SSL? Do i have a server misconfiguration?

 

[Bitpalast]

Port 587 is always associated with STARTTLS. Port 465 is for SSL/TLS. That is the correct setting. Port 587 ought not to work with SSL/TLS, but only with STARTTLS.

 

[Ricotosh]

Hello guys, very new to PLESK. I have it on DO but cant get my mails to work, reason port 25 is blocked for the same.
Who has a solution to this.

 

[ChrisCP]

Maybe hosting provider is blocking port 25. Ie Ionos do that. So you have to ask your provider to unblock.

 

[nkomarov]

Port 587 is always associated with STARTTLS. Port 465 is for SSL/TLS. That is the correct setting. Port 587 ought not to work with SSL/TLS, but only with STARTTLS.

Can I check it anywhere in Plesk? Haven't found any settings page for that. Any extension that would show diagnostics? Or maybe an external service that would scan standard ports?
My mail client (bloody MS Outlook for Windows) can't connect to my mail server and the error message is unclear so I'm struggling to find out where to fix.

 

[mow]

My mail client (bloody MS Outlook for Windows) can't connect to my mail server and the error message is unclear so I'm struggling to find out where to fix.

Let me guess: Outlook 2019?
You can get to the old mail account configuration by opening the old system.cpl app and then E-Mail. This will give you the old mail setup where you can actually make the necessary configuration settings.
Oh, and Outlook 2019 will fail if your own domain is IDN, because it requires SMTPUTF8 and so the test mail will fail and you can't complete account setup.
It seems Microsoft doesn't really want to support normal mail anymore, at least not on your own machine, and long-term wants to force everyone towards outlook.com.

 

[nkomarov]

Another reason for Outlook to refuse the connection: if in the SSL/TLS settings the Plesk admin forces "Recommended by Mozilla standards". It enables too new cipher modes that MS Outlook just doesn't support yet (while all the modern browsers do).