There are 2 issues here.
The first is that (for legacy spam handling reasons) Forward DNS needs to match reverse DNS. IE lets say I have a mail server mail.example.com. When mail.example.com sends an email to a server, that server will (using DNS) convert mail.example.com to an IP address, then convert that IP address back to a domain name, then convert the result back to an IP address. In that way the receiving mail server knows the system adminstrator of the sending mail server has some claim to the IP address as they control reverse DNS. (Im skeptical of the practicality of this test in todays Internet, but that is what is failing. Most likely because reverse DNS is not set up for the IP address in question)
The second ussue is - whrn a mail server connects to another server to send an email, the first thing it sends is a command like "helo xxxxxx" or "ehlo xxxxxx" - xxxxxx being the domain name of the sending server. xxxxxx is set wrong on the sending server above. This should be fixable by changing the configuration of thr sending mail server to set its hostname so the helo response is correct.
Be aware that if the sending mail server has thrse basics wrong there are likely a nimber of other factors working against it which will frustrate mail delivery as well (like low volumes, possibly a bad reputation, and things like SPF records might be missing as well. It might be better to relayail thriugh a trusted mail server to remove thr hassle ilof maintaining a mail server - as the amount if work to set up a small and large mail server the same, and it is a fair amount of work to get right.