User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1.2 Safari/605.1.15

Steps to reproduce:

The size of the attachment (PDF file) is not determined in the received letter.

1. I forward the letter with an attachment to another address;
2. A letter comes to another address without this attachment (!).

Thunderbird 91.1.2 versions have been tested for both Windows and macOS. If the original letter is forwarded in a different way (by other mail client like Roundcube), then the size is determined correctly and the attachment appears in the forwarded letter.

Actual results:

The forwarded email does not contain the original attachment.

Expected results:

The forwarded email must contain the original attachment.

Can you reproduce it with any attachment files or a specific pdf file?

When forwarding, can you try File -> Send Later, then go to the Outbox folder, see if the message contains attachment.

This reproduces with this specific PDF file. If there is another ones, not known.

Is it possible to share this pdf file so I can try to reproduce? Can you download a nightly version from https://ftp.mozilla.org/pub/thunderbird/nightly/latest-comm-central/thunderbird-94.0a1.en-US.win64.zip, and see if it's the same.

Unfortunately, I cannot transfer the PDF itself, since its contents constitute a trade secret of the company. And I'll try the beta version.

Hi Victor, this is unlikely to be a bug in Thunderbird. Maybe something odd about the MIME structure of the message (what you call "letter") which you're forwarding. We need a lot more detail from you for this to go anywhere...

Forwarding a message with attached PDF works for me on TB 91.1.2 (64-bit), Win10. Reported against Mac.
Victor, can you please try the following steps exactly, to inspect the outgoing message in your own outbox?

• with your trouble-PDF
• then with another PDF (from a different source)

STR

1. Right-click on message A with subject "hello world" and attachment-1.pdf
2. From context menu, select Forward As > Inline (!)
3. In composition window of message B (Fwd: hello world), add recipient
4. File -> Send Later (!)
5. Check message B in your own Thunderbird, Local Folders > Outbox
6. Double-click on attachment-1.pdf of Message B in outbox

Actual = Expected

• Outbound message B in outbox contains attachment-1.pdf
• attachment-1.pdf opens and shows up correctly.

• After step 2, are you still seeing attachment-1.pdf in composition window? Can you open attachment-1.pdf from there with double-click? (The temporary PDF was renamed to nsmail.tmp in my case, but could be opened as a PDF)-
• After step 6, can you open attachment-1.pdf from message B in your own outbox?
• What makes you think that this has anything to do with determining the size of attachment? Did you inspect the code?
• What happens if in step 4, you CC yourself - does your own received copy of message B still have the attachment-1.pdf?
• Any screenshots that you can make available (use graphic editor to black out sensitive data) and attach here via Attach New File button above comment 0?