Pode ser possível suprimir a mensagem não executando no modo daemon.
De link :
The workaround would be to use a shell script to emulate the "" mode, and not use it (because the e-mail warnings only get sent in daemon mode). You may have to use grep -v to kill the message there, too, if you don't want it in the logs (not shown in the example below) and redirect the remainder of the output into the log file, such as:
while true ; do
fetchmail >>/home/users/srolinso/fetchmail/log/fetchmail_etg.log \
-d0 \
-f /home/users/srolinso/fetchmail/fetchmail_etg
sleep 10
done