I have a similar work-flow, but I made a shell function for that (an "alias") called `email`:

    email ()
    {
        export TMP_EMAIL_FILE=$(mktemp -t email_XXXXXXXXXX.eml) && vim -c 'set filetype=mail' -c 'set tw=72' -c 'set spell' "${TMP_EMAIL_FILE}" && {
            cat "${TMP_EMAIL_FILE}" | xsel -ib
        }
    }

Feel free to copy, use and modify it. :)