Although a class macro name can be any ASCII character (any character in the range 0x0 to 0x7f), avoid using any of the nonletter characters. At the very least they create confusing reading, and at worst they can cause sendmail to completely misinterpret your intentions.
Although values can traditionally be made to contain whitespace by
quoting them, class macros will misinterpret those quotes. For
"vax ds1" wrongly parses into two class
the quotes a part of each.
Duplicate values are silently ignored. Therefore, typos in a list of values can cause an accidentally duplicated entry to be silently excluded.
Avoid creating a new class macro name without first checking to see
whether it has already been used. That is, don’t
create a list of UUCP hosts within class
without first checking both for preexisting
FU definitions and for
rule-set uses of
It is perfectly legal for the
$~U expressions to exist in rule sets without a
definition. However, such empty references will still cause
sendmail to search the string pool.
Under V8 sendmail you can watch your class macro
definitions being formed by using the
debugging switch (-d37.8). Under other versions
of sendmail you can only approximate this
information by using the
-d36.9 debugging switch.
The file form’s scanf(3) pattern can produce unexpected results. Remember that the pattern is applied to a line, not to a stream.
No error ...