mutt 1.7.2-1+deb9u1 from Debian stretch segfaults when piping a message? Turns out to be related to 860176, at least for me.

The following patch on top of the 1.7.2-1+deb9u1 source package fixes the segfault for me:

Index: mutt-1.7.2/imap/message.c
===================================================================
--- mutt-1.7.2.orig/imap/message.c
+++ mutt-1.7.2/imap/message.c
@@ -508,7 +508,7 @@ int imap_fetch_message (CONTEXT *ctx, ME
	  }
	  else
	    pbar = NULL;
-	  if (imap_read_literal (msg->fp, idata, bytes, &progressbar) < 0)
+	  if (imap_read_literal (msg->fp, idata, bytes, pbar) < 0)
	    goto bail;
	  /* pick up trailing line */
	  if ((rc = imap_cmd_step (idata)) != IMAP_CMD_CONTINUE)