iOS S/MIME Encryption Issues 16.6

I am having an issue where S/MIME on my iOS 16.6 device is half working. I am able to receive/read encrypted emails and can send signed messages without issue. I am also **able to send encrypted emails**, but **only if it is a reply to another party**'s signed email. I cannot, for anyone, send a new email that is encrypted, regardless of the fact that I have their certificate installed and their signature trusted. **I am even unable to send myself a (new) encrypted email** to my own email address (the same as sender) on iOS as it says “Unable to encrypt”. I tried reinstalling my S/MIME certificate (.p12) as well and the certificates of other parties, but nothing changed. What makes even less sense is that, provided the other party emails me first (with a signed email), I can reply to their signed message and it will let it encrypt; it also works just fine for if they send me an encrypted message (I can reply, encrypted). It works 100% on macOS (I can send new encrypted mail etc. without it needing to be a reply). I have tried: * Installing root/intermediate certificates for SSL.com (my cert provider), Entrust * Ensuring that the default account is the one with S/MIME (per the Apple Discussion iOS Mail S/MIME cert installed and trusted but “No valid certificates found” and double-checking I did it right by the article How to change the default email account on your iPhone in 4 steps ) * Disabling mail privacy settings * Enabling encryption for all outgoing mail (Entrust’s documentation said that was part of install) I rebooted between all of these steps just on the off chance it was a caching issue. Still nothing. Has anyone run into this before? How did you get it working? I am absolutely stumped and have spent hours trying to figure this out.