Newline in To: field not handled

Handling the following fails when using mini_sendmail but works fine when sending directly to Postfix
...
From: test <x@xx.com>
To: m \<m.mmmmmmm@mmmmm.com>, r \<r.rrrrr@rrrrr.com>, b
 \<b.bbbbbbbb@bbbbb.com>, w \<w.wwwww@wwwww.com>
Subject: Message
...