Hi Elizabeth,
You can have a smart campaign that listens for leads added to your static list (i.e. Newsletter only).
Trigger = Added to list "Newsletter only"
Flow = Change Data Value "Marketing Suspended" // New Value = TRUE
This essentially acts as an unsubscribe (but you control it) - they will still receive operational emails, but be blocked from non-operational marketing emails.
Discussion here. Please note though, if a lead was already unsubscribed = true, they will still be blocked from emails regardless.
When are you ready to send out your email, just include a step or smart campaign to change data value "marketing suspend = FALSE" for your static (newsletter only) list, and change back to TRUE after your email blast. Let me know if you have questions. Thanks!