Note that only parentheses can be nested. None of the other balanced pairs can nest.
You have already seen the quoted string and comments. The angle brackets (< and >)
are used to specify a machine-readable address, such as
. Th e
square brackets ([ and ]) are used to specify a direct Internet address (one that
bypasses normal DNS name lookups), such as [123.45.67.89].
The sendmail program gives warnings about unbalanced characters only when it is
attempting to extract an address from a header definition, from the header line of a
mail message, or from the envelope. Beginning with V8.6, when sendmail finds an
unbalanced condition, it tries to balance the offending characters as rationally as
possible. Regardless of whether it can balance them, it prints one of the following
warning messages:
Unbalanced ')'
Unbalanced '>'
Unbalanced '('
Unbalanced '<'
Unbalanced '"'
If it did not succeed in balancing them, the mail will probably bounce.
25.4 ?flags? in Header Definitions
The name part of the H configuration command can be prefixed witha list of flags.
This list, if present, must be surrounded by ? characters:
H?flags?name:field
Table 25-2. Balancing characters
Begin End
??? ???
( )
[ ]
< >
This is the Title of the Book, eMatter Edition
Copyright ?© 2007 O??™Reilly & Associates, Inc. All rights reserved.
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