Hello rich82. I'm curious can it be that PDF you're trying to attach is trying to attach itself inline, not as a file? I don't know is it possible to attach PDF inline on Thunderbird at all, but this could be the problem. Can't reproduce it on my PC, it's attaching as file for me (see an image). Could you please go to Tools > Preferences > Config Editor and check if (these are mine settings):

• mail.content_disposition_type is set to 1
• mail.file_attach_binary is set to false

Also check:

• pdfjs.disabled is set to true

gacuxz - Thanks for your prompt response.

The first two parameters were already set as you suggest. The latter was "false", so I changed it to "true", but the problem persists. Any other ideas?

Thanks!

Perhaps try windows safe mode with networking as see if the hang persists in that mode. My experience is most of these hangs are caused by antivirus products just being to slow in their scanning of files. Given they pay particular attention to PDF and office documents as they are known virus vectors often these issues only affect those file types.

Problem solved. It was the virus scan of PDF files that caused the hang. Thanks to both of you!