I suspect your auditors have no real reason to object to Let's Encrypt (do they understand that Let's Encrypt is equally capable of issuing a false certificate under your name? does your security rely on the browser PKI? how did every single company in the browser PKI get okayed by your auditors?).

You have a perfectly valid reason, which is that your auditors want you to buy an expensive certificate to make them happy, but you're still paying more than market ($0ish) for SSL, which means you're a good customer for DigiCert to have acquired.

BTW, if you want to save some money, try sending your auditors the WebTrust audits that Let's Encrypt has passed just as well as Symantec (if not more well, see mozilla.dev.security.policy): https://letsencrypt.org/repository/

As you can probably imagine, money isn't an issue. Our budget for our PKI team is larger than a small startup's entire annual payroll cost.

The checkboxes you're implicating here are the ceremonial kind. (I do security in the financial infrastructure space, for whatever that's worth).

I suppose we'll agree to disagree (RegSCI in this case). Happy to grab a beer if you want to lecture me on how I'm wrong, I try to be open minded.

Whether it's ceremony or not, I have to check the box or face harsh regulatory penalties.

Happy to do this over beer, but I'm not sure I understand which of the SCI rules would determine which CA you use.

I'm a little amused (not at you, but at the absurdity of the whole process) that we're talking about CA selection for products that almost definitely can't even properly quote and unquote a FIX field separator from user input.

What about Let's Encrypt certificates make them non compliant to your auditors?

they didn't pay several million dollars to get added to the checklist

Maybe they pin to the CA certificate? In that case, it matters how much you trust the specific CA.