1 qmail-smtpd     Receive message by SMTP from another host:

     2                    

     3      |             MAIL FROM:<joe@heaven.af.mil>

     4      |             RCPT TO:<bill@irs.gov>

     5      |          

     6      |          Is $RELAYCLIENT set? Yes: "".

     7      |          Accept RCPT.  

     8      V             

     9                    

    10 qmail-queue     Store message safely on disk.

    11                 Trigger qmail-send.

    12      |             

    13      V             

    14                    

    15 qmail-send      Look at envelope recipient, bill@irs.gov.

    16      |          Is irs.gov in locals? No.

    17      |          Is bill@irs.gov in virtualdomains? No.

    18      |          Is irs.gov in virtualdomains? No.

    19      |          Is .gov in virtualdomains? No.

    20      |          Deliver remotely to bill@irs.gov.

    21      V          

    22                    

    23 qmail-rspawn    Run qmail-remote.

    24 

    25      |             

    26      V             

    27 

    28 qmail-remote    Look at host name, irs.gov.

    29                 Is irs.gov listed in smtproutes? No.

    30 		Look up DNS MX/A for irs.gov and connect to it by SMTP:

    31                    

    32                    MAIL FROM:<joe@heaven.af.mil>

    33                    RCPT TO:<bill@irs.gov>