Why is my mac.com email address suddenly receiving hundreds of reg.ru emails daily?

I've always received some level of phishing and junk emails, but in the past month I am suddenly receiving 50-100 from a foreign url daily. I no longer use my mac.com email address and have set up a rule to move them into the trash.

However, I'm concerned that me.com & iCloud.com emails may also become compromised. Reg.ru appears to be a valid hosted email system in Bulgaria. Has anyone else had this problem? Since I have not used my mac.com address for years, how did it suddenly get compromised? Is Apple aware of the problem?