Being a mail router, sendmail does not provide a user
interface for composing and sending mail.
These tasks are handled by a Mail User Agent (MUA).
The standard MUA on SCO OpenServer systems is the
SCO Shell Mail.
With sendmail configured and using one of the standard
SCO OpenServer MUAs, whether mail, scomail,
The user composes a piece of mail with an MUA.
The MUA uses execmail
to transfer the mail to sendmail.
execmail executes a new instance of
sendmail and passes any command-line
flags and options it received from the MUA on to
These flags and options, along with the contents of the
/usr/lib/sendmail.cf file, control the operations of
this instance of sendmail.
sendmail collects the recipient address(es) prior to
collecting the entire message and parses the address(es) to determine the
appropriate mailer and any aliases, forwarding addresses, or expanded
sendmail collects the message.
sendmail either stores the message in the queue for
delivery later or
calls upon the appropriate mailer to deliver the message now.
If additional MUAs are added to the system, they may
request mail routing from sendmail by
a new instance of sendmail directly without
going through execmail, or using SMTP
directly to the local host.
How sendmail works
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003