Yup -- that's what the spec says. See, in particular, 4.1.1.2, which
gives the syntax of the MAIL FROM: command, and 4.1.2, which gives the
syntax of a Reverse-path.
There are some SMTP servers which don't require the <>, but they're
being generous -- they've always been required.
--Steve Bellovin, http://www.research.att.com/~smb