sendmail, 4th Edition

Quoted Strings in the Header Field

Recall that quotation marks (") force arbitrary text to be viewed as a single atom. Arbitrary text is everything (including joined lines) that begins with the first quotation mark and ends with the final quotation mark. The following example illustrates two quoted strings:

"Full Name"
"One long string carried over
        two lines by indenting the second"
   ↑
   whitespace

The quotation mark character can appear inside a quoted string only if it is escaped by using a backslash:^[438]

"George Herman \"Babe\" Ruth"

Internally, sendmail does not check for balanced quotation marks. If it finds the first but not the second, it takes everything up to the end of the line as the quoted string.

When quotation marks are used in an H configuration command, they must be balanced. Although sendmail remains silent, unbalanced quotation marks can cause serious problems when they are propagated to other programs.

^{[438] *} Note that the backslash itself cannot appear within full quotation marks.