Spam is REJECTED and not deleted. In cause of a possible false positive the sender (!) will receive a non delivery report. Deleted e-mails is always forbidden.
It is not exactly clear (on the website) what you mean by 'rejected', so the English text could be improved to make your meaning more explicit. Perhaps 'returned' would be better?
In a technical language, "rejecting" (I don't accept that message) and "bouncing" (I accept it, but I will send it back later) is clear defined. Returning would be "bouncing", because I do NOT return, I do NOT ACCEPT.
They should be slightly more explicit, but "...before the e-mails are accepted and reject anything that looks suspicious..." almost certainly means that spam is rejected with a 5xx message - or goes to your InBox, but is never accepted then hidden from you in a spam folder.
It's a good approach, and from a legal perspective I'm surprised more systems don't take this approach, because legally (at least in my local jurisdiction), you're deemed to have received an email when it "enters that information system" - i.e. when your SMTP server says 250.
This stuff matters quite a lot in the formation of contracts.
Yes, but the "bounce message" comes to the sender from their own mail system, saying "could not deliver".
This is important, because the receiving system doesn't have a guaranteed way of reaching the sender - modern spam typically fakes the "From:" and <return-path> fields - so well-run systems nowadays never try to do so for fear of generating what's referred to as email backscatter spam.
My interpretation is: Spam is deleted in order to give you plausible deniability that you haven't received and read it.
i.e. There is no spam folder.
But, this seems like it would normally be a bug rather than a feature.