So you have your “likely to sell” list. The next step is to append phone numbers to your contact information. There are a ton of services that do this; just Google “append phone numbers” and find a service that offers verified information. If you have the option to pay more for verified emails, I recommend you take the offer. After all, there isn’t much point in sending out mass emails to a bunch of dead addresses.
Once you append emails to your addresses, take your list and upload it to a service such as Never Bounce. These programs scrub your list of any bad emails, so you can verify that your information is good.
Now you’re all set up to send cold emails. So what are cold emails? They shouldn’t be spam, but they are unsolicited. As long as it’s a personal email, there’s nothing wrong with sending them out. Popular services like Mailchimp don’t like sending out emails en masse, so I wouldn’t recommend relying on them.
I also recommend creating a separate, non-domestic email to send your messages. Don’t use firstname.lastname@example.org; use something like Google Workspace instead. Purchase a separate domain name, and authenticate yourself so that your emails don’t head to the spam folder.
Beyond authentication, there are a few things you can do to make your emails more personal. First, upload a picture of yourself and attach it to your profile. Let people know you’re a real person. Next, include your full signature in all your emails. These are little things, but they go a long way in making you seem more authentic.