DISABLE EXPAND

TCP/IP-channel-specific options: DISABLE_EXPAND (0 or 1)
The SMTP EXPN command is used to expand mailing lists. Exposing the contents of mailing lists to outside scrutiny may constitue a breach of  security for some sites. The SMTP server option , when  set to 1, disables the EXPN command completely, causing the SMTP server  to issue the response 550 5.7.2 EXPN command has been disabled to any EXPN command. The default value is 0, which causes the EXPN command to work normally.

See also the ,  , and    channel options that can be used to control this behavior on a per-channel, rather than  per-SMTP-server, basis. And see the  MTA option which sets an MTA-wide default.

Note that mailing list expansion can also be blocked on a list-by-list basis with the Unified Configuration alias options   and ,  or the &#x5b;EXPANDABLE&#x5d; and &#x5b;NONEXPANDABLE&#x5d; alias file named parameters.

Note that an LDAP attribute named by the   MTA option  (normally set to the attributes   and   ) can also be used to disable expansion on a  list-by-list basis (and can be used on user entries as well).

See also:
 * expnallow Option
 * expndefault Option
 * expndisable Option
 * expandable_default MTA Option
 * Alias file named parameters
 * ldap_expandable MTA Option
 * alias_expandable Option
 * alias_nonexpandable Option
 * TCPIP-channel-specific options