The title pretty much sums it up.
Arguably you can use many different mail server software solutions, including Postal, for cold emailing but spam-like activity is highly likely to get you in trouble with your server provider or blocked by various email services or both so is unwise as an activity.
If I say no, will this stop you from doing it?
To be more serious, Postal is designed for sending and tracking transactional emails. It's fairly good at doing so in large volumes, and plenty of people use it for things like mailing lists, but there are likely better tools for mass-sending marketing emails.
I guess I'm more asking the question: Would it work well?
When cold emailing properly (not getting flagged for spam & being engaging, relevant, and personalized) it's important to have an email sending server that has the ability to drip. So mass-sending, at least all at once, is not really what I want to do.
Basically, this just means the ability to pace the volume of emails that go out. For instance, if I was using a brand new domain and sending IP, I would want to "warm it up" - I'm hoping I can interact with Postal's API this way.
That way, I could create a piece of software that sent out, perhaps only 50 emails the first day, 60 the next, until capping out at 200 emails a day. Maybe even spreading the sending of those emails out throughout the day.
Also, I wanted to include this because I feel like I'm getting judged a little lol:

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If I say no, will this stop you from doing it?