What's the number in square brackets, in the maillog for?

Here are some lines of my maillog. What are those numbers in square brackets telling me? Is that a pid for each individual email i get?

So [11342] for example, belongs to the same message right?

postfix/smtpd[11342]:   connect from
postfix/smtpd[11342]:   Anonymous   TLS
policyd-spf[11350]: prepend Received-SPF:
postfix/smtpd[11342]:   NOQUEUE:    reject:
postfix/smtpd[11342]:   disconnect  from
postfix/smtpd[11342]:   connect from
postfix/smtpd[11342]:   Anonymous   TLS

Solution 1:

It's the PID of the process:

Jun  6 17:47:17 eli postfix/smtpd[27410]: disconnect from unknown[122.114.65.210] ehlo=1 auth=0/1 quit=1 commands=2/3       
$ ps aux | grep 27410                    
postfix  27410  0.0  0.0  44524 10812 ?        S    17:46   0:00 smtpd -n smtp -t inet -u -c -o stress= -s 2

Depending on configuration, a single process may handle more than one message.