using terms from application "Mail"
    on perform mail action with messages theMessages for rule thisRule
        repeat with theMessage in theMessages
            tell theMessage
                try
                    set font of content to "Helvetica"
                on error e number n
                    my logit("OOPs: " & e & " " & n, "MailScript")
                end try
            end tell
        end repeat
    end perform mail action with messages
end using terms from

to logit(log_string, log_file)
    do shell script ¬
        "echo `date '+%Y-%m-%d %T: '`"" & log_string & ¬
        "" >> $HOME/log_" & log_file & ".log"
end logit