Q: Can send from @mac.com - but cannot receive @mac.com

So i've had my @mac.com for years - though my @mac.com account; was dormant and haven't used it in a few years...I noticed when I went to iCloud.com it upgraded it to an @icloud.com account but also listed my three emails @mac.com, @me.com and @icloud.com - As it should.

So I can send a message from @mac.com in iCloud.com, Mac Mail.app and iOS Mail App...shows up just fine - but when anyone tries to respond to it they get a Mail Delivery System - Mail delivery failed

I even tried sending a message from @icloud.com to @mac.com and it doesn't even receive the message or a delivery error 0 but shows up in sent messages.

Any idea if @mac.com is no longer receivable?

Thank you!

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