Worst you could ever expect.
Never ever use them! I have just created a mail account for one purpose: to link a second authorisation from a storage provider. Never ever sent a single email from them. Received only few confirmation emails from my storage provider. Then boom, account is temporarily blocked due to suspicious activity. I couldn't understand, what activity? It's just 10 minutes old! It tells I should get in touch with customer support. OK, I sent them a message. After 24 plus hours I get a response, that they regret to inform me, but I breached their terms. How? When? In 10 minutes without a single email sent and receiving two from the international company? Their email was obviously simply automated response, most likely they don't have enough staff to deal with anything, or just lazy.
Normally, I wouldn't care at all, but it literally caused me 300$ damage, just 10 minutes! NEVER EVER TRUST MAIL COM AND THEIR PARENT COMPANY 1&1
Recommendation: Do you care about your email? Go somewhere else. Mail.com is totally unpredictable with worst customer service out there