Rules that hide hosts in a domain should
be applied only to sender addresses. Avoid the temptation to place
such substitutions of hosts for domain names into the
canonify rule set 3. The
canonify 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
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.