Where a blocked message goes
Blocking is a decision about the reply, and it says nothing about what happens to your text. Services differ: some discard it, some log the event, some keep the message for review, and some count repeated blocks against the account. The page that describes the filter rarely describes this.
People treat a block as the end of the exchange. From the service side it is often the start of a record, and that record is a separate question from the one you were asking.
On this page
The event is usually logged
Even a service that discards message text tends to record that a block happened, with a timestamp and a category. That log exists for tuning the filter, and it is the minimum most services keep. Discarding the text and keeping the event are compatible, and a page saying nothing is stored may mean exactly this.
Some services keep the message
Reviewing a sample of blocked messages is how a filter gets improved, and improvement needs examples. Where this happens, the text of a blocked message is more likely to be read by a person than the text of an ordinary message. That inverts the usual expectation, which is worth knowing before pasting something sensitive to test a filter.
Repeated blocks can reach the account
Some services count blocks and act on a threshold: a warning, a restriction, a suspension. Where this exists it is described in the terms rather than on the product page. A service with no account has no place to attach such a count, which is a structural difference rather than a policy difference.
How to find out
Read the terms for the words moderation, review and enforcement rather than reading the product page. A service that names what it keeps and for how long has told you something; a service that describes only what the filter does has answered a different question.
Before you type
Is a blocked message safer than a message that was answered?
Often the opposite, because blocked messages are the ones worth reviewing. Assuming a block means the text was thrown away is the common mistake.
Does a service without accounts still log blocks?
It can log the event without being able to attach it to a person. The event and the identity are separate things, and only the second needs an account.
Can I ask a service what it kept?
Where a data request process exists, yes. The answer covers what is attached to your account, so a service with no account has nothing to return.
Read what a service keeps before you test what it blocks.
Open no filter chat