SPF allows up to 10 DNS calls. We use multiple email providers and overall get 13 DNS calls for SPF.
The solutions I've found so far:
Manually collecting and "inlining" the IP addresses to reduce DNS lookups. Unfortunately this makes the entry static and will not be up-to-date when providers update their SPF records.
Creating subdomains for one/few of the SPF providers - won't work for business reasons.
Using an "SPF proxy" - I found only spfproxy.org (now defunct?) and I'm afraid to use them because I can't find who is behind it and they don't answer emails.
What options do I have? Ideally a solution like spfproxy which I can trust would work for me but I could not find any.