How best to send binaries by an autoresponder?

I want to add the ability to attach binary files, specifically Excel
speadsheets and Word documents, to a response by an autoresponder.

I would prefer to mime encode when the file is sent so the files can be
updated at any time, but if it works betters by pre-encoded and then
treating the file as simple text, that would be alright.

Thanks for any suggestions.
Don