I can receive, but not send emails using iCloud Custom Email Domain after DNS change

After making a recent DNS change, I get the error "Sender address rejected: Domain not found" whenever attempting to send emails from the Mail app using my iCloud Custom Email Domain. I've double-checked my DNS setup should be correct, and have copied across all previous records (MX, TXT etc.). I'm able to receive emails on the domain, but sending has been giving the same error for a few hours.

So far, I've tried:

• Sending from iPhone, Mac Mail app and iCloud webmail (all fail)
• Seeing if I can "re-verify" the domain anywhere in iCloud admin, but the option doesn't appear anywhere
• Adding another sender address, and sending as that. The address shows up in my client, but I get the same error when sending.

I'm hoping something just needs to propagate, because the only other option I can think of is to remove the domain, and set it up again. I don't want to do this, because I don't want to lose all emails.

Is there anything else I can try to fix this?