A line that begins with either a tab or a space character is considered a continuation of the preceding line. Internally, such continuation lines are joined to the preceding line, and the newline character of that preceding line is retained. Thus, for example,
DZzoos lions and bears line begins with a tab character
is internally joined by sendmail to form
DZzoos\n lions and bears newline and tab retained.
Both the newline (
\n) and the tab are retained.
When such a joined line is later used (as in a header),
the joined line is split at the newline and prints as two
separate lines again.