Traffic logs

Use the -X flag of the sendmail command to set traffic logging.

Many Simple Mail Transfer Protocols (SMTPs) implementations do not fully implement the protocol. For example, some personal computer-based SMTPs do not understand continuation lines in reply codes. These can be very hard to trace. If you suspect such a problem, you can set traffic logging by using the -X flag. For example:

/usr/sbin/sendmail -X /tmp/traffic -bd

This command logs all traffic in the /tmp/traffic file.

Because this command logs a lot of data very quickly, it should never be used during normal operations. After running the command, force the errant implementation to send a message to your host. All message traffic in and out of sendmail, including the incoming SMTP traffic, will be logged in this file.

Using sendmail, you can log a dump of the open files and the connection cache by sending it a SIGUSR1 signal. The results are logged at LOG_DEBUG priority.