Write the action you want in the subject line.
I was in a conversation with a client where we spoke about an email I had sent them. Because the subject line was the usual subject line (that only sent an FYI message every week) but the content was way more, they did not open the email.
While I had thought “they would read the email anyway”, their understanding was that since there was no actionable, there was no point reading it.
I won’t tout for their action to be right, however, it isn’t wrong either.
When in doubt, overcommunicate.