How can I delay Qmail sending when NFS or NIS is faulty?

Article Title: how to delay Qmail sending when there is a problem with NFS or NIS. Linux is a technology channel of the IT lab in China. Includes basic categories such as desktop applications, Linux system management, kernel research, embedded systems, and open source.
If the user directory is on NFS or the user information is stored on NIS, the Qmail system will send a message as if the user does not exist when the NFS server or NIS server fails, how can this problem be solved?
Create a Qmail user database on the local machine, so that Qmail will no longer find the user's home directory and password database. this operation involves three steps:
1. first, store all user lists (including local and NIS passwords) to/var/qmail/users/passwd.
2. run
# Qmail-pw2u-h </var/qmail/users/passwd>/var/qmail/users/assign
Here-h means that all users must have the home directory. if it happens to run this command when an NFS problem occurs, an error message is displayed and the command is stopped.
3. run
# Qmail-newu
Remember to regenerate the database if the user changes.