Cold Email 101

This is slightly embarrassing to admit, but I have no idea where to start with cold email.

Here's where I'm at currently - and my apologies for the lengthy post, but I figure I'll get more detailed feedback if I actually provide a detailed explanation of the problem(s).

I run marketing for a small company (less than 15 employees). One part of the business that desperately needs revamped is our cold emailing process. My team most likely cold emails over 100,000 people/year because of the scope of our business (B2B).

Before I took over marketing, the previous person used a popular email service to do cold outreach, but was list-cycling (a big no-no) to keep the total number of contacts lower than they otherwise would be. Deliverability of these emails was terrible (not even the test emails would end up in OUR inboxes when sent for proofing), most likely because they were sending graphics-heavy HTML emails. If memory serves, we were paying nearly $800/mo for the service, so I cancelled it.

I want to send plain-text emails to prospects. I assume that I'll most likely have to use something like Instantly.AI or some variation of a cold-emailing service. Our lists are extremely clean (I have one employee that focuses 100% of their time doing list management).

Here is where I need help: 1. How do I determine how many domains we need to send from? 2. Do subdomains perform well? I'd assume that sending an email from "[email protected]" would rarely result in an open. 3. What are some solid cold email platforms that you personally recommend that ALSO won't break the bank? 4. For whatever platform we decide to use, do I need to actually sign up for an account that can handle 100,000 contacts, or can I rotate the lists in/out based on time of year and location (we serve over 30 markets in the US, but only sell to them for a few months at a time each year)?