The DANE TLSA record for incoming mail is not set (v26b)

Hi
Dis an upgrade to v26b (hardly blinked and a new upgrade)
I seem to have gone from a lot of green ticks to a new ‘?’

The DANE TLSA record for incoming mail is not set. This is optional.

It was a green tick before the upgrade. Has something failed?

How do I set it? What do I set it to?