Hi, can anyone tell me how to approve or reject a vendor bill through email without a netsuite login because the approver doesn't have access?

You can use Suiteapproval suiteapp's email approval feature. Note that this add-on is free to install. Lookup Suiteapproval in suiteanswers for more info.

@Sam-I-Am do you know for sure if email approval works for employees that don't have access? I haven't tried this myself but saw conflicting info online