Problems sending to external domains

[alento]

Are the delivery issues limited to only gmail?

I have not followed the discussion of the MTA-STS issue, but you can find the discussion here:

[SOLVED] V0.50 MTA-STS policy is missing: STSFetchResult.NONE

I can confirm that no action is required, just wait for 24 to 48 hours and DNS records will propagate automatically across DNS servers and the errors will disappear. No need to issue Let’s Encrypt certificates or anything.