test should be sent through the
server bigserver.example.org. The 0 indicates the numeric priority for this MX record. When
more than one MX record exists for a given label, the MX with the lowest priority is tried first. If a
temporary error is encountered, the next highest priority mail server is tried, and so on until the
NOTE
674
Running Servers Part V
list is exhausted. At that point, the sending server will keep trying periodically until the message
times out (generally five days). If multiple MX records exist with the same priority, they are tried in
a random order.
Most mail servers will also fall back on the IP address listed in the A record for a label in
the event that no MX records exist. However, it is considered bad practice to rely on this.
In some cases, it may be complicated to establish an A record because your IP address frequently
changes. Obviously, this is not suitable for commercial purposes, but there is a workaround that
is acceptably reliable for personal use. This is achieved through dynamic DNS services that are
available (often at no charge) through a number of different companies. A list of these companies
is maintained at http://dmoz.org/Computers/Software/Internet/Servers/Address_
Management/Dynamic_DNS_Services/.
Pages:
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245