Ordinarily, V8 sendmail forces envelope-sender route addresses^[28] to be enclosed in angle brackets. But beginning with V8.7 sendmail, angle brackets can be omitted by specifying F=d.

^[28] Also see the DontPruneRoutes option in DontPruneRoutes, and how route addresses are handled in rules in Section 19.3.3.

Under some circumstances it is possible for these angle-bracketed addresses to be given to a shell, causing them to be wrongly viewed as I/O redirection. This problem is most common with the UUCP and prog delivery agents.