I have found that the site https://mxtoolbox.com/ is very good for scanning your records for SPF/DMARC/DKIM and pointing out problems. Unfortunately even with implementing all of this some email providers are heavy handed with rejecting mail from smaller mail servers. For instance Yahoo will usually block all of your mail without appealing to them, and Verizon will not allow any email originating from a VPS source like Digital Ocean or AWS. Ironically I found that out when going to report someone on Verizon's network trying to brute force my SMTP server. Mail to abuse was rejected.