There are a number of configuration parameters you may want to change, depending on the requirements of your site. Most of these are set using an option in the configuration file. For example, the line O Timeout.queuereturn=5d sets option Timeout.queuereturn to the value 5d (five days).
Most of these options have appropriate defaults for most sites. However, sites having very high mail loads may find they need to tune them as appropriate for their mail load. In particular, sites experiencing a large number of small messages, many of which are delivered to many recipients, may find that they need to adjust the parameters dealing with queue priorities.
All versions of sendmail prior to 8.7 had single character option names. As of 8.7, options have long (multi-character names). Although old short names are still accepted, most new options do not have short equivalents.
This section only describes the options you are most likely to want to tweak; read section