I am receiving several timeout error messages from the F-PROT milter.

This problem is most likely due to a lack of system resources. Antivirus scanning can be quite resource intensive. Sendmail/milter is designed not to add unnecessary pressure on the mailserver during times of high load.

If the milter plug-in seems unresponsive to Sendmail, it will cancel the pending job. Sendmail will then return "451 Please try again later" to the peer mailserver to indicate it has a temporary problem in processing e-mails.

Sendmail's default timeouts used are insufficient for f-prot-milter. Make sure you have this as your configuration line in sendmail.mc (to activate the change you must compile a sendmail.cf file and restart sendmail):

INPUT_MAIL_FILTER(`f-prot-milter', `S=inet:12200@127.0.0.1, F=T,T=E:8m;C:5m;R:4m;S:2m')

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