I've been using MailWarm for the last few months, and this tool is amazing! Whether you need to simply have a better score/reputation for your cold emails or just for your new domain (new business for example), this is the perfect tool for you. I think that everyone that creates a new email address should use it in the beginning so you're not falling in the junk folder right away.
Also, their support and team is really nice and responsive, as well as open to suggestions to improve their platform.
I would suggest you to not miss their current deal, as, for now, I don't know any alternative tools in the market that does that and that does it as well.