Courses, consulting and mentoring is the niche where DM campaigns get used most often, and most often wrongly.
Why cold DMs barely work here
Someone who has never heard of you receives a message offering education. They do not know who you are and cannot see why you should be trusted with money and time. Conversion approaches zero and accounts burn quickly: complaints land on exactly this kind of message.
The constraint is not technical, it is substantive. Selling education means selling trust, and trust cannot be delivered in a first message.
The two-step alternative
Cold contact brings the person somewhere you already demonstrate competence: a channel, a teardown, a free resource. The campaign then goes to people who have read you — an entirely different conversation.
The numbers differ by multiples: a campaign to a warmed list converts well enough for the model to close; to a cold one it does not.
Costing it
Two spends instead of one: bringing people into the list, and working the list. The second costs almost nothing and repeats many times — the same list serves several launches. So the figure to track is not cost per sale but cost per list subscriber and the number of sales the list produces in a year.
The first message
Even to a warm list, the opener decides most of it. Specificity and a reason work: why you are writing now, and to this person. A template does not, because it reads as a campaign — which it is. Segmenting by what someone read and writing per segment beats one message to everyone for the same effort. The mechanics and limits are on the automation page.