even though such messages violate the SMTP protocol.
.SH "CONTROL FILES"
.TP 5
+.I addrcheck.cdb
+A database of acceptable mailboxes. If present, this is used to report
+erroneous RCPT TO commands, which can reduce the amount of junk mail
+accepted. It contains an encoding of the virtual domains map
+.RB ( \c
+.BI V domain
+maps to
+.IR prefix ),
+the local domains
+.RB ( \c
+.BI @ domain
+maps to an empty string), and the available local parts
+.RB ( \c
+.BI L mailbox
+maps to
+.B +
+if the address is valid or
+.B \-
+if not). It's best made using
+.BR qmail-valid-addresses (8).
+.TP 5
+.I addrcheck-delay
+Delay in seconds before reporting bad mailbox names after the
+.I addrcheck-slow
+limit is reached. The default is 2.
+.TP 5
+.I addrcheck-limit
+Number of bad mailbox names to tolerate before dropping the connection.
+Zero means an infinite number. The default is 50.
+.TP 5
+.I addrcheck-slow
+Number of bad mailbox names to tolerate before imposing delays. The
+default is 5.
+.TP 5
.I badmailfrom
Unacceptable envelope sender addresses.
.B qmail-smtpd
.B qmail-smtpd
will reject
any envelope recipient address with a domain not listed in
-.IR rcpthosts .
-
-Exception:
-If the environment variable
-.B RELAYCLIENT
-is set,
-.B qmail-smtpd
-will ignore
-.IR rcpthosts ,
-and will append the value of
-.B RELAYCLIENT
-to each incoming recipient address.
+.I rcpthosts
+unless the sending host is a designated relay client (see the
+description of the
+.I relayhosts
+file beow).
.I rcpthosts
may include wildcards:
Envelope recipient addresses without @ signs are
always allowed through.
.TP 5
+.I relayhosts
+Allowed relay clients. Each line is a host-suffix pair, separated by a
+colon. If the client's hostname matches one of the hostnames in the
+file, that client is permitted to send mail to any host (i.e., to use us
+as a relay), and the corresponding suffix is appended to all recipient
+addresses generated by the client.
+
+.I relayhosts
+may include wildcards:
+
+.EX
+ heaven.af.mil:
+ .heaven.af.mil:
+ hell.irs.gov:.irs.virtdomain
+.EE
+
+For historical reasons, the
+.B RELAYCLIENT
+environment variable overrides this table. If
+.B RELAYCLIENT
+is set, it has the same effect as there being a matching entry in the
+.I relayhosts
+file, using the value of
+.B RELAYCLIENT
+as the suffix.
+.TP 5
.I smtpgreeting
SMTP greeting message.
Default: