Many Internet providers allow small sites (such as home machines) to dial up when there is a demand for network traffic to flow. Such connections are usually of short duration and use the PPP or SL/IP protocols. A problem can arise when this dial-up-on-demand is instigated by sendmail.^[21] The process of negotiating a dial-up connection can take so long that sendmail will have its attempt to connect(2) fail. (See also the connect keyword for the Timeout option in See this section). To remedy this situation, V8.7 and later offer the DialDelay option. It is declared like this:

^[21] Or by any other network-oriented program, such as FTP or a web browser.

O DialDelay=delay           configuration file (V8.7 and later) 
-ODialDelay=delay           command line (V8.7 and later) 
define(`confDIAL_DELAY',delay)  mc configuration (V8.7 and later) 

The argument delay is of type time. If this option is entirely omitted or if delay is omitted, the default is then zero and no delay is enabled. The default for the mc configuration technique is also zero. If the unit of time is omitted from the time declaration, the default is seconds.

If delay is nonzero and sendmail has its initial connect(2) fail, it will sleep(3) for delay seconds and then try to connect(2) again. Note that sendmail tries to connect again only once, so the delay should be large enough to accommodate your anticipated worst-case delay. On the other hand, care should be taken to avoid excessively long delays that can make sendmail appear to hang. No check is made by sendmail for absurdly large values given to delay.

This option was more relevant in the days of dial-out modems. With ISDN lines this option shouldn't be needed. You should need this option only if you are dialing out on an old technology modem.

The DialDelay option is safe. If it is specified from the command line, sendmail will not relinquish its special privileges.