Make sure you put a period at the end of the subject line. Their quoted text includes a period at the end.

Please also scold them for behaving unethically and perhaps breaking the law.

We just opted out. I told them our lawyers have been instructed to watch them like a hawk.

Updated!

The period is outside the quotes though, are you suggesting we should have the quotes too?

The section from the OP I'm referring to is:

    Contact us to opt out. If you want to exclude your Customer Data from Slack global models, you can opt out. To opt out, please have your Org or Workspace Owners or Primary Owner contact our Customer Experience team at [email protected] with your Workspace/Org URL and the subject line “Slack Global model opt-out request.” We will process your request and respond once the opt out has been completed.

That includes a period before inside the quotes which would suggest a period inside the subject line.

There's some shenanigans going on here, of course. The section I was looking at says...

To opt out, please have your org, workspace owners or primary owner contact our Customer Experience team at [email protected] with your workspace/org URL and the subject line ‘Slack global model opt-out request’.

That's weak. Be better, Slack.

For reference, I got an email back saying I was opted out and a bunch of justifications about why it's okay what they did and zero mention of the legality of opting people in by default.

I don't think this is shenanigans, just inconsistent use of English rules. I'd be floored if a judge ruled the period was pertinent here; there's no linguistic value or meaning to it (i.e. the meaning of the message is the same with or without it).

I'd be very surprised to hear that Slack was allowed to propose a free-form communication method, impose rigid rules on it, and then deny anyone who fails to meet those rigid rules. If Slack was worried about having to read all of these emails, they should have made a PDF form or just put it on a toggle in the Workspace settings. This is a self-inflicted problem.