Message body being scanned, message censored ( bounced), no unsafe content....?

[#1]

I sent an e-mail to a correspondent in academia. We were talking about DNSSEC.
I included this link
https://www.dnssec-validator.cz
which is a browser plugin that examines every https connection and tells you whether there is a DNSSEC record, whether it is bogus and whether the TLS certificate chain is intact. This is work originating from the Czech equivalent of  the UK ISP association; it surely is 100% respectable
So why the bounce ? How did the signature get in the e-mail scanner database in the first place ?

[#2]

Not directly relevant, but I know my brother, who has a lot of Czech contacts, sees (or at least used to see?) an unrepresentatively large proportion of emails from .cz addresses put into spam by Yahoo mail; presumably because being from a .cz address is in itself seen as suspicious.

[#3]

Just tried a test e-mail again. Surely it can't *still* be bouncing ?
It [Censored] is.
Unbelievable.
Dick:red Avoidance of swear filter edited as per forum rules.

[#4]

That URL is showing as clean now, so I'm assuming the problem is no more?

[#5]

Yes, it works now, but my original fix was simply to turn on S/MIME encryption in Thunderbloat so your broken, nosey scanner couldn't read my correspondence.

[#6]

Quote from: disfroot

Yes, it works now, but my original fix was simply to turn on S/MIME encryption in Thunderbloat ...

That's only simple if you've the recipient's key