MailShake just works, and is a pleasure to use. The price is very reasonable and there are some really good guides on their site for how to do email outreach and more. If I had one feature request it would be to integrate with Google Sheets so I don't have to download a CSV and then upload it to MailShake, but that's a minor niggle.
I used Mailshake for years before joining the team to help it grow. Coming from a sales background I used many tools to cold email. Mailshake is the most simple tool and extremely effective from a Gsuite email.
In addition to closing dozens of eCommerce consulting deals, I was able to get free accommodation in Bali by emailing resorts and offering to exchange drone footage. Very versatile tool because you can simply add in more mail accounts.