1 files changed, 7 insertions, 2 deletions

diff --git a/mailutils/sendmail.c b/mailutils/sendmail.c
index a216d66c1..2f99df6c0 100644
--- a/mailutils/sendmail.c
+++ b/mailutils/sendmail.c
@@ -229,10 +229,15 @@ int sendmail_main(int argc UNUSED_PARAM, char **argv)
                         rcptto(sane_address(s+5));
                         free(s);
                         // N.B. Bcc: vanishes from headers!
+
                 // other headers go verbatim
-                // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
-                } else if (strchr(s, ':')) {
+
+                // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
+                // Continuation is denoted by prefixing additional lines with whitespace(s).
+                // Thanks (stefan.seyfried at googlemail.com) for pointing this out.
+                } else if (strchr(s, ':') || (list && skip_whitespace(s) != s)) {
  addheader:
+                        // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
                         if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
                                 goto bail;
                         llist_add_to_end(&list, s);