# --- T2-COPYRIGHT-BEGIN ---
# t2/package/*/bincimap/bincimap-1.3.4-macandmime.patch
# Copyright (C) 2004 - 2026 The T2 SDE Project
# SPDX-License-Identifier: GPL-2.0 or patched project license
# --- T2-COPYRIGHT-END ---

Please try this patch and see if it helps.
Jerry Lundström

Index: bincimap-1.3.4/src/mime-printdoc.cc
===================================================================
--- bincimap-1.3.4/src/mime-printdoc.cc	(revision 347)
+++ bincimap-1.3.4/src/mime-printdoc.cc	(working copy)
@@ -58,7 +58,7 @@
   }
 
   mimeSource->reset();
-  mimeSource->seek(headerstartoffsetcrlf);
+  mimeSource->seek(headerstartoffsetcrlf + startoffset);
 
   char c;
   for (unsigned int i = 0; i < length; ++i) {