Note that comments are only valid in mail headers, but not smtp.
Generally even besides CFWS related differences there are some differences in between which email addresses SMTP allows and which are allowed in mail headers....
Lastly given that quoting in the local part as well as some special forms of the domain part are not supported by most programs it's often sensible to reject them, i.e. treat them as invalid even through technically they are not. (But you really should support internationalized mails!)
Generally even besides CFWS related differences there are some differences in between which email addresses SMTP allows and which are allowed in mail headers....
Lastly given that quoting in the local part as well as some special forms of the domain part are not supported by most programs it's often sensible to reject them, i.e. treat them as invalid even through technically they are not. (But you really should support internationalized mails!)