Is do_not_reply@apple.com an official apple email

The official Apple email address in question would not have the underscores in it. If you put them there simply to show the email address without making it a working link, then yes, donotreplyatapple.com is a real Apple email address.

I type “at” rather than use the @ sign.

That account is one from which Apple sends out notifications for which replies are not required but it is a real address because it says "@apple.com".

I check the real origin of an email by clicking Reply and clicking on the tiny arrow beside the name of the sender. The arrow reveals the real address which the email came from and to which a reply will go. This is worth doing even with accounts you trust, especially with accounts you trust. Of course, I do not reply to addresses which do not match the pretended addresses.