User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:79.0) Gecko/20100101 Firefox/79.0

Steps to reproduce:

Tested with two different accounts in Thunderbird (78.2.0 (64-bit)):

1. work-account
   The sender is using in Thunderbird, IMAP, outlook.office365.com, port 993, SSL/TLS
   The sender is forwarding e-mail to receiver.

2. university-account
   The sender is using in Thunderbird, IMAP, outlook.office365.com, port 143, STARTTLS
   The sender is forwarding e-mail to receiver.

Actual results:

1. The receiver is using Outlook in browser and Outlook app in phone - does not see the content in forwarded e-mails.
   ONLY with Outlook desktop, the forwarded e-mails can be read by the receiver.

2. The receiver is using Outlook in browser and Outlook app in phone - does not see the content in forwarded e-mails.
   ONLY with Outlook desktop, the forwarded e-mails can be read by the receiver.

The issue is that receiver does not see the content of the forwarded e-mails when sender uses IMAP and server outlook.office365.com

In both cases, when the sender is forwarding e-mail through the browser, the e-mails can be read by the receiver correctly, in full.

Expected results:

Receiver should see the content of the forwarded e-mail.

In both cases, when the sender is forwarding e-mail through the browser, the e-mails can be read by the receiver correctly, in full.

The issue started after upgrading Thunderbird to version 78. The issue may be related of moving also from 32bit to 64bit, not sure. In any case, the problem has been continuing now for one or two months (from June/July 2020).

Confirm this bug.

This bug is also on Exchange 2016 CU 18 ...

I think you're seeing bug 1675507. Will be fixed in 78.6.

(In reply to Magnus Melin [:mkmelin] from comment #3)

I think you're seeing bug 1675507. Will be fixed in 78.6.

Do you agree the problem is gone?