Hi Heliohost team,
I am using K-9 Mail and Thunderbird Beta on my Android phone and I seen a lock icon being crossed out in most of the email messages I received, as shown below.
I checked at my TLS settings for ajhalili2006.heliho.st (where I pointed the MX records for andreijiroh.dev) if I missed anything and seems everything is fine. Also can I enable MTA-STS for Heliohost Mail per this specific Google Workspace docs page?