Some changes I made at the direction of an agent: fix domainkeys CNAMEs for M365, rotate M365 dkim keys that haven't been rotated for over a decade, fix broken spf record formatting.
My biggest issue is that squarespace refuses to enable dkim signing for transactional emails that they send for us (order/shipping confirmation etc). The email sending service they use (socketlabs) supports it but they are not interested in enabling the feature, so I can't lock down our dmarc. I guess that means squarespace is not a good fit for our needs; it's just disappointing that we have to move to a different platform again for technical reasons that are solvable with a dashboard switch.