echanism :: Parser Encoding
mechanism = stringCI "7bit"             *> pure Binary7Bit
       <|>  stringCI "8bit"             *> pure Binary8Bit
       <|>  stringCI "binary"           *> pure Binary
       <|>  stringCI "quoted-printable" *> pure QuotedPrintable
       <|>  stringCI "base64"           *> pure Base64
       <|> (Encoding <$> x_token)
       <|> (Encoding <$> ietf_token)

mechanism :: Parser Encoding
mechanism = stringCI "7bit"             *> pure Binary7Bit
       <|>  stringCI "8bit"             *> pure Binary8Bit
       <|>  stringCI "binary"           *> pure Binary
       <|>  stringCI "quoted-printable" *> pure QuotedPrintable
       <|>  stringCI "base64"           *> pure Base64
       <|> (Encoding <$> x_token)
       <|> (Encoding <$> ietf_token)
mechanism = stringCI "7bit"             *> pure Binary7Bit
       <|>  stringCI "8bit"             *> pure Binary8Bit
       <|>  stringCI "binary"           *> pure Binary
       <|>  stringCI "quoted-printable" *> pure QuotedPrintable
       <|>  stringCI "base64"           *> pure Base64
       <|> (Encoding <$> x_token)
       <|> (Encoding <$> ietf_token)