MailerCheck is the best, but I used also Hunter in the past and it did its duty pretty well. Source: over 1 year ago

MailTracker for Gmail is free but it only shows you if the email has been opened. Source: over 2 years ago

Hunter mailtracker - Email tracker to see if/when/how often customer/ investors see your emails. Source: almost 3 years ago

Hunter Mail Tracker: This is a classic. Bring “WhatsApp” read checks to your email. Know each time your email gets opened. Period. Source: almost 3 years ago

I use Soverin: https://soverin.net/ which lets you create multiple mailboxes on the same 3.25/month package. - Source: Hacker News / about 1 year ago

I have been using https://soverin.net. It has a privacy-first approach to email, while at the same time they are transparent in regards to its operation. They operate and are based in the Netherlands. - Source: Hacker News / almost 2 years ago

Soverin and AnonAddy are worth looking into imo. Soverin supports unlimited custom domain aliases. Source: about 2 years ago

Don’t forget the guys at https://soverin.net/ as well. Decent pricing and solid NL hosting and very private. Source: about 2 years ago