SMTP (-1) error: failed while connecting to the server from Roundcube

I have never done this and I will never do this
Sorry maybe my question was unclear

I will host with my Vps and Ispconfig, 15 domain name, each domain name have their own dedicated IP and normally the IP of my server don't need to be used for the domain name.
Actually, when I'm sending emails with my domains names, my config send all email with the IP of server1.domaine-hostname.com and not with the Ip of my domain name.
That's why I asked

Which return this if I send an email

• IP: IP of my VPS
  
• HELO: server1.domaine-hostname.com
• rDNS: IP of my VPS

 

Please just answer me, just yes or not can be ok.
With ISPConfig can I send email and get as a sender :

• IP: 123.456.789 (dedicated Ip of my domain name)
  
• HELO: mydomain.com
• rDNS: mydomain.com

Or I can only send email like that :

• IP: IP of domaine-hostname.com
  
• HELO: server1.domaine-hostname.com
• rDNS: server1.domaine-hostname.com

 

Thank you for your clear answer
I do not have your skills, mine are not enough to achieve this without help.
I started reading the documentation, but it will take me too long to find the right method.
I do not intend to make you waste your time with more explanations, maybe you have some links with tutorials that could help me learn how to use dedicated IP with Postfix ?
Thanks