29.11 Pitfalls

• Rules that hide hosts in a domain should be applied only to sender addresses. Avoid the temptation to place such substitutions of host for domain names into rule set 3. Rule set 3 applies to all addresses and can wrongly change a nonlocal address.

• Not all configuration files focus with user<@domain>. IDA, for example, uses a more complex focus: <@domain>,...,user. Be sure you understand the style of focusing that is used in your configuration file before attempting to create new rules.

• Avoid confusing rule sets 1 and 2 when adding rules. Rule set 1 is for the sender; rule set 2 is for the recipient.

• Typos in rule-set declarations can be difficult to locate. For example, S1O (in which the last character is the capital letter O) will silently evaluate to rule set 1 when you really meant rule set 10.

• All versions of sendmail except V8 wrongly call rule set 2 and the recipient R= when processing the envelope sender.