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Exchange SE HU6: PDF attachments truncated to 13 KB via Outlook Desktop — OWA unaffected
We've spent days isolating this and ruled out everything we could touch. The corruption survives agent disabling, Bitdefender removal, and BypassFiltering — and the message tracking logs show exactly...
Root cause narrowed down further:
The corruption is PDF-structure-specific. We tested two PDFs:
- Working: PDF with traditional xref table, 1 object stream → arrives intact
- Broken: PDF using only cross-reference streams (/Type /XRef), 5 object streams (/ObjStm), no traditional xref table → truncated to ~13 KB
We converted the broken PDF using pikepdf (ObjectStreamMode.disable), forcing a traditional xref table and removing all object streams. The converted version (same content, different structure) arrived intact via Outlook Desktop.
Conclusion: The X-SDDS store delivery step in Exchange SE 15.2.2562.41 fails specifically when processing MAPI/TNEF attachments that are PDFs using cross-reference streams without a traditional xref table (compact PDF 1.5 format).