May i know why, i can access my @mac apple id but i cant get the email access for this address?

The "Related Article" above your question tells what you can do with an @Mac eMail address.

says

"If you had a working @mac.com email address as of July 9, 2008, kept your MobileMe account active, and moved to iCloud before August 1, 2012, you can use @icloud.com, @me.com, and @mac.com email addresses with your iCloud account.

In each case, you can sign in to iCloud with either your @icloud.com email address or the Apple IDthat you use with your iCloud account."

Re: "May i know why ..... i cant get the email access for this address?

See this discussion thread on a similar topic for answers:

How do I access my Mac.com email? - Apple Community

Eg: says:

" go to Settings>iCloud and sign in with the ID to which that address belongs.

Mail to xxx@mac.com is the same thing as xxx@icloud.com".

and

"Have you tried going to Settings/Password & Accounts and adding the iCloud Account?

Then go to Mail to check for the email?"

All the best :-)