Here are a few of the more useful options you can set in the configuration file:
Setting this option limits the size of message that Exim will accept.
Setting this option limits the amount of an incoming message that Exim will return as part of a bounce message.
If the system load exceeds the value given for this option, all mail delivery is suspended, though messages are still accepted.
This is the maximum number of simultaneous incoming SMTP calls Exim is prepared to accept.
This option controls the amount of material that is written to the log. There are also some options with names beginning with log _ that control the logging of specific information.