Where should I draw the line between lexer and parser?

I'm writing a lexer for the IMAP protocol for educational purposes and I'm stumped as to where I should draw the line between lexer and parser. Take this example of an IMAP server response:

* FLAGS (\Answered \Deleted)

This response is defined in the formal syntax like this:

mailbox-data   = "FLAGS" SP flag-list
flag-list      = "(" [flag *(SP flag)] ")"
flag           = "\Answered" / "\Deleted"

Since they are specified as string literals (aka "terminal" tokens) would it be more correct for the lexer to emit a unique token for each, like:

(TknAnsweredFlag)
(TknSpace)
(TknDeletedFlag)

Or would it be just as correct to emit something like this:

(TknBackSlash)
(TknString "Answered")
(TknSpace)
(TknBackSlash)
(TknString "Deleted")

My confusion is that the former method could overcomplicate the lexer - if \Answered had two meanings in two different contexts the lexer wouldn't emit the right token. As a contrived example (this situation won't occur because e-mail addresses are enclosed in quotes), how would the lexer deal with an e-mail address like \Answered@googlemail.com? Or is the formal syntax designed to never allow such an ambiguity to arise?