It currently supports MIME through use of CL-MIME. It will automatically load and attach any attachments specified by pathname which CL-MIME will then automatically encode. xmls-tools is used to allow XHTML emails to be written for which text alternatives are automatically generated and included with the MIME message. XHTML emails also have any images on the local filesystem automatically loaded and attached.
CL-Sendmail is a library for sending email using the external program 'sendmail'.