SPF record is not matching rDNS for multiple domains on a single droplet

I have a droplet with LAMP stack installed. Using Plesk, I have managed to host 10 domains successfully.

Let’s say my host name is set as “myHost.local” so DigitalOcean provides me a rDNS record for that (which I don’t have access). Then I have 10 domains hosted as domain1.com, domain2.com, …, domain 10.com all with their own DNS, SSL, email and everything set properly and functioning smoothly.

Now, the problem is that when I want to set an SPF record for my emails, it will technically look like this:

“v=spf1 +a +mx +a:myHost.local include:some3rdparty.eu -all”

• Since there is no A record for that host name in every domain’s DNS records, all the emails that I send end up in recipient’s spam folder or get rejected.

• If I change the a: identifier to my domain name, then there will be a rDNS mismatch and spamming again. I even tried to set in in include: identifier and got the same result.

• If I change the host name to match my domain name, then I can fix it for only one of the domains and the problem remains for the rest.

Can anyone help me to set this up please? I feel very frustrated. :( Thanks in advance!