multiple execution of Fetchmail / Getmail causes high load
The cron for getmail is executed every 5 minutes. If there are many messages to fetch from the external mail account, 5 minutes aren't enough to finish the job. The result is that after a while, there are many parallel getmail processes who try to fetch the mails. This leads to a very high load on the system. In my case, I had to kill 5 simultan processes at a load of 8 and 45000 Mails in the postfix-queue. Postfix/Amavis weren't able to deliver the mails fast enough.