Looks like there is a rights problem modifying the body of those mails
Every time when we try to modify the HTMLBODY or BODY property we fail with MAPI_E_NO_ACCESS.
The attached mails in those tests where ms-tnef formated (winmail.dat)
omhelp.cpp:lookup_oom_dispid:160 wchar_t alloc 00000155d9abfe80:HTMLBody
07:35:08/5284/oomhelp.cpp:put_oom_string:674 wchar_t alloc 00000155ccf77710:<html><head></head><body><table border="0" width="100%" cellspacing="1" cellpadding="1" bgcolor="#0069cc"><tr><td bgcolor="#0080ff"><p><span style="font-weight:600; background-color:#0080ff;"><center>OpenPGP Nachricht</center><span></p></td></tr><tr><td bgcolor="#e0f0ff"><center><br/>Bitte warten Sie w�hrend die Nachricht entschl�sselt / gepr�ft wird...</td></tr></table></body></html>
07:35:08/5284/oomhelp.cpp:put_oom_string: Putting 'HTMLBody' failed: 0x80020009
07:35:08/5284/DBG_OOM/oomhelp.cpp:dump_excepinfo: Exception:
wCode: 0x1000
wReserved: 0x0
source: Microsoft Outlook
desc: Sie besitzen nicht die erforderliche Berechtigung, um diesen Vorgang auszuf�hren.
help: null
helpCtx: 0x0
deferredFill: 0000000000000000
scode: 0x80070005
07:35:08/5284/TRACE/oomhelp.cpp:put_oom_string:699: return
07:35:08/5284/ERROR/mail.cpp:decryptVerify_o: Failed to modify html body of item.