There are a large number of debug flags built into the sendmail command. Each debug flag has a number and level, where higher levels mean print more information. The convention is that levels greater than nine print out so much information that you would not want to see them except for debugging a particular piece of code. Debug flags are set using the -d flag as shown in the following example:
debug-flag: -d debug-list debug-list: debug-flag[.debug-flag]* debug-flag: debug-range[.debug-level] debug-range: integer|integer-integer debug-level: integer
-d12 Set flag 12 to level 1 -d12.3 Set flag 12 to level 3 -d3-17 Set flags 3 through 17 to level 1 -d3-17.4 Set flags 3 through 17 to level 4
Available debug flags are as follows: