You have sort of told us what you want to do, but not about what is stopping you.

The "how to" select Read ALL mail documentation appears to be for prior releases of Thunderbird and I can not find that option by following that advice. Problem is that I have a SPAM filter (MailWasher) that reads all my email and reduces the amount of SPAM I need to deal with significantly. Unfortunately that means that the gmail inbox has all be "read". After filtering I fire up Thunderbird and it reads from my other accounts just fine, but the gmail never gets read. This began several months (maybe 6) ago, but had been working for over a year. I am not at Thunderbird 54.something, was a 45.something when I noticed the issue. I need to set the real ALL email option, but can't find it.

If you use Gmail with IMAP then there is an "All Mail" folder which might be what you're looking for. However I normally advise users not to have this folder active in Thunderbird. It effectively repeats everything you can see in other folders. It might be handy occasionally to do some repair work, but you could enable it as needed or do the repairs via the gmail website.

However, that's IMAP and you're using POP, which knows only about the Inbox folder. So you don't have use of the All Mail folder.

It's a long time since I used MailWasher and I can't recall having this type of problem. The whole point is to screen your incoming and remove what is not wanted before it has a chance to download to your client, and so by design MailWasher ought to be able to read messages without marking them as having been read.

Have you asked in MailWasher support forms about this issue? Thunderbird is constrained by what happens at the server and what the server tells it. If your messages are being marked as read, and then the server declines to offer them to Thunderbird, it's outside Thunderbird's control.

The Thunderbird documentation clearly shows an option: "Read ALL mail" (which specifically includes mail that has been read). When I installed Thunderbird over a year ago (due to switch from XP to Win 10) this option was working. Some months ago it quit working, and I can no longer find the option in any of the settings. What am I missing.

IMHO this is NOT a MailWasher or Gmail issue (even w/o MailWasher, I often read my gmail on my iPhone), then want to download when accessed by my POP Thunderbird. I prefer to "keep" emails in Thunderbird on my PC.

Give us a link the the documentation you refer to.

Spent hours trying to find the doc which I had seen earlier with the option: "Real ALL POP email". Entering that in the search did not help However, I did find a suggestion that suggested including @gmail.com in the user name. I changed my user name to SteveRyder.com@gmail.com and now Thunderbird downloads ALL my messages.

Thanks for the response that led me to find the solution.