Interspire Email Marketer: Configure local SMTP (Postfix) on Contabo VPS to send newsletters

I have a working installation of Interspire Email Marketer on my Contabo VPS (Ubuntu 22.04 with Plesk). The system is ready but it cannot send any emails. I need an experienced freelancer to configure... (Budget: €8 - €30 EUR, Jobs: Bulk Marketing, DNS, Interspire, Linux, Plesk, Postfix, SMTP, Ubuntu)