Special routing Introduction _S_e_n_d_m_a_i_l will normally transmit email message directly to the destina­ tion host using SSMMTTPP (standard email protocol over TCP/IP). This is sometime inappropriate. You may want to "manually" override some deci­ sion 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 normal behavior. Here are some. · The destination host is not reachable from your computer. Your computer is behind a firewall. · The DNS of the destination host is buggy or incomplete (No valid MX record). · 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 a special rules to forward the messages properly. · You have a better (less expansive, faster, ...) route to this host than the default one. 22.. ttaasskkss You may have many special rules. Each rules contain 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 UUUUCCPP 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/sub-domain under it. Note that you may select this option and still provide another special routing for one host/sub-domain 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 out of this file. _L_i_n_u_x_c_o_n_f take care of this any time you save the rules. 44.. mmaaiilleerrttaabbllee iiss aann ooppttiioonn Many Sendmail do not support the mailertable mechanism. This is a compile time option and few linux's distribution have chosen not to include this feature. In the ""bbaassiicc iinnffoorrmmaattiioonn"" screen, there is a check box 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 (check-box), you must regenerate the sseennddmmaaiill..ccff file. If your _S_e_n_d_m_a_i_l fail to start after that, check the error logs in //vvaarr//lloogg. Your Sendmail may be configured to not supported the mailertable concept.