Office 365, Email, Exchange, Thunderbird, Attachment Truncated in Thunderbird, Attachment size incorrect

Thunderbird incorrectly reports the size of attachments and truncates attachments from the Exchange servers. I can't open the entire attachment from an email in Thunderbird.


Thunderbird is a free, open-source product and there isn't a vendor for us to escalate to. We will try to help troubleshoot but in the end you might need to visit forums for solutions. 

If you run into trouble and are faculty/staff you should speak with your local IT pro about using officially supported email clients.

Exchange may mis-report sizes of attachments, so Thunderbird will truncate attachments from Exchange servers unless you tell it to ignore the misinformation, as described on this website:

The steps to fix this in Thunderbird:
  1. Open Thunderbird.
  2. Open the Thunderbird Menu 
  3. Select Options
  4. Then Options Again which opens the Options Tab
  5. Select Advanced 
  6. Select Config Editor.
  7. Accept the warning.
  8. Enter "chunks" in the search box.
  9. "mail.server.default.fetch_by_chunks" appears.
  10. Double-click so Value reads "false".
  11. After changing this setting you will need to remove and reconfigure you Exchange account on Thunderbird per the instructions listed here: Office 365, Email, Exchange, Thunderbird

Keywords:Thunderbird attachment size truncate   Doc ID:48037
Owner:Office 3.Group:University of Illinois Technology Services
Created:2015-03-03 15:21 CDTUpdated:2020-02-24 11:45 CDT
Sites:University of Illinois Technology Services
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