36.5.3 EX_IOERR A System I/O Error Occurred

An exit value of EX_IOERR (the value 74) means that a serious operating system error occurred. This class of error relates mostly to disk I/O.

If the body of a mail message could not be read, the following error message is logged:

    putbody: df
    qid
    : read error

The file may have vanished because of a disk crash and may have been restored to lost+found . 
The qid is the queue identifier that will help you to find the qf file. Inside that qf file are an I line that give the inode and major and minor device 
numbers of the disk that held the df file (see Section 23.9.7, I line ).

An error that occurs while writing to the pipe (2) connection to a delivery agent causes the following error to be logged and for the fork (2)'d child to exit with EX_CONFIG:
putbody: write error