What you have to understand about mail.com is that the free mail platform is just designed to get you in the door so they can sell you their premium service.
The free platform is garbage. If the person to whom you're sending hasn't received email from you before, your message will go directly to their Spam. In addition, it doesn't support any useful signature in your outbound messages.
Then on top of that, their "support" is an insult. They won't allow you to reach out by phone and it takes days before a human will respond to a request for help, even if your email service is shut down.
In short, avoid this platform like the plague.