Current neomutt sidebar patch does change COLS which does
not work with threadsafe ncurses6. Beside this: do not
bother other non-sidebar users as well make sidebar delimeter
look well.

---
 buffy.c      |    6 +++---
 configure.ac |    8 ++++++++
 sidebar.c    |    9 ++++++++-
 3 files changed, 19 insertions(+), 4 deletions(-)

--- configure.ac
+++ configure.ac	2016-05-31 11:15:58.082946555 +0000
@@ -313,6 +313,14 @@ main ()
                 if test x$mutt_cv_curses != x/usr; then
                         LDFLAGS="$LDFLAGS -L${mutt_cv_curses}/lib"
                         CPPFLAGS="$CPPFLAGS -I${mutt_cv_curses}/include"
+                fi
+                if test -d /usr/include/ncurses5 ; then
+                        if test -d /usr/lib64/ncurses5 ; then
+                            LDFLAGS="$LDFLAGS -L/usr/lib64/ncurses5"
+                        else
+                            LDFLAGS="$LDFLAGS -L/usr/lib/ncurses5"
+                        fi
+                        CPPFLAGS="$CPPFLAGS -I/usr/include/ncurses5"
                 fi])
 
 	AC_CHECK_FUNC(initscr,,[
--- buffy.c
+++ buffy.c	2016-05-31 12:24:04.232839516 +0000
@@ -756,10 +756,10 @@ int mutt_buffy_check (int force)
       buffy_check(tmp, &contex_sb);
     sb_set_update_time();
   }
-#else
-  for (tmp = Incoming; tmp; tmp = tmp->next)
-    buffy_check(tmp, &contex_sb);
+  else if (!option (OPTSIDEBAR))
 #endif
+    for (tmp = Incoming; tmp; tmp = tmp->next)
+      buffy_check(tmp, &contex_sb);
 
 #ifdef USE_NOTMUCH
   for (tmp = VirtIncoming; tmp; tmp = tmp->next)
--- sidebar.c
+++ sidebar.c	2016-05-31 11:52:28.873409292 +0000
@@ -643,6 +643,7 @@ draw_divider (int first_row, int num_row
 {
 	/* Calculate the width of the delimiter in screen cells */
 	int delim_len = mutt_strwidth (SidebarDividerChar);
+	int altchar = 0;
 
 	if (delim_len < 1)
 		return delim_len;
@@ -653,12 +654,18 @@ draw_divider (int first_row, int num_row
 	if (delim_len > SidebarWidth)
 		return -1;
 
+	if (delim_len == 1 && strcmp(SidebarDividerChar, "|") == 0)
+		altchar++;
+
 	SETCOLOR(MT_COLOR_DIVIDER);
 
 	int i;
 	for (i = 0; i < num_rows; i++) {
 		move (first_row + i, SidebarWidth - delim_len);
-		addstr (NONULL(SidebarDividerChar));
+		if (altchar)
+			addch (ACS_VLINE);
+		else
+			addstr (NONULL(SidebarDividerChar));
 	}
 
 	return delim_len;