How to increase email deliverability with subdomain virtual servers

Hi,

This is not a support request specific for virtualmin but in case someone here already faced this problem and have a solution, that could be great.

I'm trying to increase email deliverability with subdomain virtual servers by implementing right spf records.

Actually, our DNS are hosted on GoDaddy and we have a wildcard record there in DNS records for a domain, lets name it exemple.com

so, this wildcard * point to @ and @ is pointing to ip 1.1.1.1

when we create virtual servers on our virtualmin box for subdomains, like test.exemple.com , we have nothing to do except to setup the virtual server to point to 1.1.1.1

Now, about SPF. We have an SPF record that allow 1.1.1.1 for the domain exemple.com inside the DNS records but we dont have SPF record for test.exemple.com

When i check some analysis results, i see that most of my traffic donc pass the SPF, probably because of this reason because most of the emails are sent from those subdomains that are not listed.

Maybe i'm wrong and it's not the good reason but i'm trying to find some solutions.

Do you think i must create a SPF record for each subdomain under the DNS of exemple.com ?

I see that GoDaddy has an API to manage DNS, so maybe we could make a script to automate DNS update when we create a virtual server for a subdomain..

If you have some ideas/solutions for me, that will be appreciated.

Thanks