Clients can provide you the email copy text in various formats: in PSD files, Word documents, Excel spreadsheets, PDF's and even Illustrator files. Very often, that text contains invisible Unicode characters, such as line end symbols, which look broken in the final email ("�" for example).
It is a best practice to encode all the special characters before pasting them into the email HTML code. For example, pound sign needs to be encoded into
Detergent fixes all of that and more. It is the most comprehensive tool on the market (currently) to convert and prepare any text into email HTML-friendly code.