The xdelay= syslog equate shows the amount of time the current total transaction took. This could be the amount of time the message took to be transmitted during its successful, final delivery, or the amount of time the message took to be deferred because of a transient error. This differs from delay= in that delay= shows the total amount of time the message took, computed from when the message was originally received or queued (this could be days ago), until it was eventually delivered.

In the case of SMTP mail, the xdelay= computation starts when sendmail starts trying to connect to the remote host. In the case of locally delivered mail, the computation starts when sendmail executes the delivery agent. The computation ends when the dot is accepted at the close of the DATA SMTP phase or when the local delivery agent exits, and is typically a few seconds.

The form of the xdelay= looks like this:

xdelay=HH:MM:SS

The time expression shows the hours (HH), minutes (MM), and seconds (SS) it took to perform delivery via the final delivery agent. In the case of networked mail, that interval can be long but usually isn't:

xdelay=00:41:05   sometimes a bit long
xdelay=00:00:02   usually swift

But in the case of locally delivered mail, this interval can seem instantaneous:

xdelay=00:00:00

Note that the xdelay= syslog equate is shown only for recipient records.