sendmail, 4th Edition

MinFreeBlocks

Define minimum free disk blocks V8.1 and later

The ESMTP SIZE keyword to the MAIL From: command tells V8 sendmail how big an incoming message is in bytes. If the SIZE keyword is not specified, sendmail assumes that the incoming message is zero bytes in size. In either case, it calls an internal routine to see whether enough space is available in the queue to accept the message. Unless sendmail is told otherwise, it assumes it can use 100% of the disk space in the queue. If SIZE bytes will overfill the queue disk, sendmail prints the following error and rejects the mail message:

Insufficient disk space; try again later

Note that the SIZE keyword (if received) is just an estimate that allows oversized mail to be rejected early in the ESMTP dialog. V8 sendmail still properly diagnoses out-of-space conditions when it actually reads the message.

If using 100% of the disk space is unacceptable, you can use the MinFreeBlocks option, the forms of which follow, to reserve space for other kinds of files:

O MinFreeBlocks=minblocks                       ← configuration file (V8.7 and
later)
-OMinFreeBlocks=minblocks                       ← command line (V8.7 and later)
define(`confMIN_FREE_BLOCKS',minblocks)         ← mc configuration (V8.7 and
later)
Obminblocks/maxsize                             ← configuration file (deprecated)
-obminblocks/maxsize                            ← command line (deprecated)

Here, minblocks is of type numeric and is the number of disk blocks you wish to reserve. If minblocks is missing or negative, or if the entire option is omitted, no blocks are reserved. ...