I don't know why the window is blank, as I don't experience the same issue. But I question why you are forwarding sent messages, as it makes more sense to me to Edit As New Message from the context menu.

When you forward a received message, the original sender is shown in the forwarded content, which might be relevant to the recipient. But if you forward a message to B that was first sent by you to A, A's address is shown in the forwarded content. Which might be an unintended result.

Thank you for your reply.

You are right, I am mostly using the beautiful feature "Edit as New". (Only in some cases I want to forward stuff from my Sent items, it happens occasionally.)

However, even the "Edit as New" feature also broke with last update. When trying to Edit as New, I also get the same behavior I described with Forwarding: The message window opens with only the subject line filled-in (and mail addresses in this case) but without content or attachments. It happens mainly to recent mails as I described earlier.

In this case I also get a yellow message which started showing up (see screenshot), although I have not changed anything in TB configuration. Everything used to work fine... The message goes like that:

"A unique identity matching the From address was not found. The message will be sent using the current From field and settings from identity John Doe <jdoe@example.com>". (Note: Real identity info has been modified for obvious reasons.)

I read multiple threads on the Internet from TB users who have reported this error in the past, but the behavior they described was not identical to the one I am facing.

I am really confused on what else I can do.

Your advice will be appreciated.

Thanks, Nick

That kind of error often means the folder is acting like a Drafts folder. Install FolderFlags and check the affected folders:

https://support.mozilla.org/en-US/questions/1460237

Hi sfhowes,

Thank you very much for your concern and advice.

I had also found (on the Internet) this advice, but please note that the behavior of "Edit as New" or "Forward" functions is not consistent, as I described, because it occurs on only part of the messages in the Sent folder (esp. the most recent) and not on all of messages in the Sent folder; therefore, the indicated thread does not seem to be relevant, because in that case the erratic behavior occurs on all messages in the affected folder.

In any case, I installed the FolderFlags plugin and checked the flags of Drafts, Inbox and Sent folders; I found that they are all correctly set as expected (Drafts, Inbox and Sent respectively).

As I was writing these lines, I thought I could try to disable any plugins and check. So, I disabled the only plugin I am using (XNote++) and everything started working fine! {Edit: Actually, further testing refutes this argument; Odd behavior continues even after disabling XNote++.}

Thanks, Nick

Sorry guys,

Further tests show that the issue has NOT been resolved by disabling XNote++. I'll edit my earlier post.

Sorry for not having tested more before I report that the issue was resolved.

So, I am back to the starting point: What may be the cause that triggers the issue with "Edit as New" or "Forward" functions to only a number of messages and not to others?

More brainstorming needed I am afraid.

Thanks, Nick

If the issue is only with some messages in a folder, try Repair Folder from Properties in the folder context menu.

As I described (see my first message), this was the very first thing I tried.

Any other ideas?

Thanks, Nick

Do a test in a new profile with just the affected account. Help/Troubleshooting Info, about:profiles. The current profile is preserved, and if the new one works properly, you can transfer data from the old to the new. Doing this will probably be more effective and faster than trying to debug the current profile.