If you start sendmail, something like this appears:
*** Warning: File 'virtusertable.db' has modification time in the future (2003-01-13 11:57:26 > 2003-01-13 06:04:40)
make: warning: Clock skew detected. Your build may be incomplete.
This means that when you install Linux, the above error judgment may occur for some time! As a result, your sendmail-related configuration file is newer than the current time, that is, the file is "from the future"~ At this time, you can use:
Touching /etc/mail/*
or synchronizing the server time can also solve this problem.