It is possible to buffer xf files in memory,^[75] and to not flush those files to disk until they exceed a specified size limit. That maximum buffered size limit is specified with this XscriptFileBufferSize option:

^[75] With V8.10 and V8.11, this option could be used only on systems that defined the confSTDIOTYPE build macro (confSTDIOTYPE) as torek.

O XscriptFileBufferSize=limit          configuration file (V8.10 and later) 
-OXscriptFileBufferSize=limit          command line (V8.10 and later) 
define(`confXF_BUFFER_SIZE',limit)     mc configuration (V8.10 and later) 

Here, limit is of type numeric. If limit is less than or equal to zero, no buffering is performed (all xf files are immediately placed on disk when opened). When limit is greater than zero, all xf files are held in memory (not placed on disk when opened), until the amount of data buffered exceeds limit. Only then is the file created and placed on disk.

Buffered file I/O is beneficial for use with the xf files. They are usually empty (because most mail succeeds), and creating and removing them from disk can impede performance. At risk is only the loss of some bounce mail error information.

The default if the XscriptFileBufferSize option is not declared, or if the limit is omitted, is 4096 bytes. The default for the mc configuration file is to not declare this option.

The XscriptFileBufferSize option is not safe. If specified from the command line, it can cause sendmail to relinquish its special privileges.