how to tell send that the mail is from dist

Hi,

The man page of dist(1) says:
    ...This  annotation will be done only if the mes-
       sage is sent directly from dist.  If the  message  is  not
       sent  immediately  from  dist,  "comp -use" may be used to
       re-edit and send the constructed message, but the  annota-
       tions  won't  take  place. ...

My question is, how does send know that the mail is from dist? What does
it mean, `sent directly from dist'?

Thanks,
Moshe