''MAX...'' '''

MAX...

Redefine maximums

port, edit specific files

When porting sendmail to a new system or tuning it for special needs, you might need to adjust one of sendmail's pre-defined maximums. These cannot be tuned in your Build m4 file. Instead, each needs to be changed in the file indicated by the third column of Table 3-7. In general, maximums should never be changed in either direction without first examining the code for possible side effects. Check to see if any minimums are required or if any warnings about maximums are evident in the code or in a README file. Some of these limits are defined by RFC, and should not be changed from the standard set by the appropriate RFC.

Table 3-7. Compile-time macros to redefine maximums
Compile-time macro	Default	File	Maximum
DEFAULT_MAX_RCPT	100	sendmail/conf.h	Initial max RCPTs per envelope (V8.12 and above)
ENHSCLEN	10	sendmail/conf.h	Length of enhanced status code^[5]
MACBUFSIZE	4096	sendmail/conf.h	Expansion of a defined macro
MAXALIASDB	12	sendmail/conf.h	Number of alias databases
MAXATOM	200	sendmail/conf.h	Atoms (tokens) in an address
MAXBADCOMMANDS	25	sendmail/srvrsmtp.c	Bad SMTP commands (V8.12 and above)
MAXDAEMONS	10	sendmail/conf.h	Ports on which to listen
MAXDNSRCH	6	sendmail/domain.c	Possible domains to search
MAXETRNCOMMANDS	8	sendmail/srvrsmtp.c	ETRNs before slowdown (V8.12 and above)
MAXFILTERMACROS	50	sendmail/conf.h	Macros per milter command (V8.12 and above)
MAXFILTERS	25	sendmail/conf.h	Milter filters (V8.12 and above)
MAXHDRSLEN	32768	sendmail/conf.h	Size of a message header
MAXHELOCOMMANDS	3	sendmail/srvrsmtp.c	HELO/EHLOs before slowdown (V8.12 and above)
MAXHOSTNAMELEN	256	sendmail/conf.h	Length of a hostname^[5]
MAXINTERFACES	512	sendmail/conf.h	Interfaces to probe at startup
MAXKEY	128	sendmail/conf.h	Length of a database key
MAXLINE	2048	sendmail/conf.h	Length of an input line
MAXLINKPATHLEN	131072	sendmail/conf.h	Symbolic link expansion
MAXMACNAMELEN	25	sendmail/conf.h	Length of a defined macro name
MAXMACROID	0377	sendmail/conf.h	Macro ID number (don't change)
MAXMAILERS	25	sendmail/conf.h	Number of delivery agents
MAXMAPSTACK	12	sendmail/conf.h	Size of sequenced map stack
MAXMIMEARGS	20	sendmail/conf.h	Arguments per `Content-Type:` header
MAXMIMENESTING	20	sendmail/conf.h	MIME multipart nesting
MAXMXHOSTS	100	sendmail/conf.h	Number of per-host MX records
MAXMIMENESTING	20	sendmail/conf.h	Multipart MIME nesting depth
MAXNAME	256	sendmail/conf.h	Length of a name
MAXNOOPCOMMANDS	20	sendmail/srvrsmtp.c	NOOPs, etc., before slowdown (V8.12 and above)
MAXPRIORITIES	25	sendmail/conf.h	Number of Priority lines
MAXPV	40	sendmail/conf.h	Arguments to a delivery agent
MAXQFNAME	20	sendmail/conf.h	qf filename length
MAXQUEUEGROUPS	50	sendmail/conf.h	Number of queue groups (V8.12 and above)
MAXRESTOTYPES	3	sendmail/conf.h	Number of resolver timeout types
MAXRULERECURSION	50	sendmail/conf.c	Rule set recursion
MAXRWSETS	200	sendmail/conf.h	Number of rule sets
MAXSHORTSTR	203	sendmail/conf.h	Length of a short string
MAXSYMLINKS	32	sendmail/conf.h	Number of symbolic links in a path
MAXTIMEOUT	(4 * 60)	sendmail/srvrsmtp.c	Timeout for slowdowns (V8.12 and above)
MAXTOCLASS	8	sendmail/conf.h	Message timeout classes
MAXUSERENVIRON	100	sendmail/conf.h	Environment items per delivery agent
MAXVRFYCOMMANDS	6	sendmail/srvrsmtp.c	VRFY/EXPNs before slowdown (V8.12 and above)

^[5] Don't change this maximum. It is defined by an RFC.

Also see QUEUESEGSIZE (QUEUESEGSIZE) and SYSLOG_BUFSIZE (SYSLOG_BUFSIZE) for a discussion of two other definitions that affect sizes.

Note that there are no debugging switches for displaying compiled maximums. If you are running a binary distribution and a maximum is of concern, you should get the source and build sendmail yourself.

Beginning with V8.12, sendmail offers several macros that slow down sendmail to prevent certain types of attacks. They are listed in Table 3-8, which also shows their default settings. Unlike the MAX... compile-time macros shown in Table 3-7, these can be tuned as part of your Build m4 file. For example, to change the maximum number of NOOP SMTP commands that can be received before sendmail slows itself down defensively, you can add the following line to your Build m4 file:

APPENDDEF(`conf_sendmail_ENVDEF', `-DMAXNOOPCOMMANDS=30 ')
                                                      
                                    increase from the default of 20

Table 3-8. Compile-Time Macros for Maximum Bad SMTP Commands
Compile-time macro	Default	Maximum
MAXBADCOMMANDS	25	Unrecognized SMTP commands
MAXETRNCOMMANDS	8	ETRN commands
MAXHELOCOMMANDS	3	HELO and EHLO commands
MAXNOOPCOMMANDS	20	NOOP commands
MAXTIMEOUT	(4 * 60)	Sleep time (seconds) after too many bad commands
MAXVRFYCOMMANDS	6	VRFY commands

If any of these SMTP-limiting compile-time macros are defined with a zero value, the corresponding check is disabled. There is no debugging command-line switch to display defaults with a precompiled sendmail. If you need to change any of these default settings, you must download and build sendmail yourself.

''MAX...'' '''

Table 3-7. Compile-time macros to redefine maximums

Table 3-8. Compile-Time Macros for Maximum Bad SMTP Commands