Special routing _S_e_n_d_m_a_i_l will normally transmit email messages directly to the desti- nation host using SMTP (the standard email protocol over TCP/IP). This is sometimes inappropriate. You may want to "manually" override some decisions made by sendmail. 11.. DDiiffffeerreenntt rreeaassoonnss ffoorr ddooiinngg ssppeecciiaall rroouuttiinngg There are many technical reasons why one would want to take control over _s_e_n_d_m_a_i_l_'_s normal behavior. Here are some: +o The destination host is not reachable from your computer. Your computer is behind a firewall. +o The DNS of the destination host is buggy or incomplete (no valid MX record). +o The host is reachable by UUCP only. You get this situation when one has a valid domain, but no direct connection to the _I_n_t_e_r_n_e_t. Your computer might be the designated Mail eXchanger for this domain. As such, it will receive all email for this domain. It will need special rules to forward the messages properly. +o You have a better (less expansive, faster, etc.) route to this host than the default one. 22.. TTaasskkss You may have many special rules. Each rule contains the following information. DDeessttiinnaattiioonn This is the destination domain you want to control. FFoorrwwaarrddeerr This is the host which will receive (and retransmit) the messages for the destination domain. The forwarder can be a fully qualified name or a UUCP name depending on the mailer used to reach that forwarder. MMaannaaggee ssuubb--ddoommaaiinn iiddeennttiiccaallllyy This rule may apply to a destination domain and all machines/subdomains under it. Note that you may select this option and still provide another special routing for one host/subdomain of this domain. This rule will take precedence over this option. mmaaiilleerr You pick the mechanism which must be used to reach the forwarder. 33.. FFiilleess The rules are stored in the file /var/lib/mailertable. The utility /usr/sbin/makemap is used to create an indexed database from of this file. _L_i_n_u_x_c_o_n_f takes care of this any time you save the rules. 44.. mmaaiilleerrttaabbllee iiss aann ooppttiioonn Many versions of Sendmail do not support the mailertable mechanism. This is a compile time option and few Linux distributions have chosen to include this feature. In the "basic information" screen, there is a checkbox to enable support for it (special routing database). If you enter some routing in the table, Linuxconf will warn you if the feature has not been selected. Once you have selected the feature (the checkbox), you must regenerate the sendmail.cf file. If your _s_e_n_d_m_a_i_l fails to start after that, check the error logs in /var/log. Your sendmail may not be configured to support the mailertable concept.