Unable to move message to Sent folder

[JD]

Hi All,
I tried to move a message to the Sent folder
(why? will explain later).
I got a banner from Thunderbird:
The folder Sent is full, and can't hold any more messages. To make room 
for more messages, delete any old or unwanted mail and compact the folder.


So, I looked at the very latest message's "Order Received", which is one
of the "sorting" tabs you can click on to display your messages, such as by
subject, sender, date .... etc.
The very latest message has the offset 2097456846.
This number is supposed to be thebyte offset within
the Sent file where the message begins.
But this offset is totally bogus.To wit:

$ pwd
/home/jd/.thunderbird/Profiles/zvdfhtln/Mail/pop.gmail.com
$ ls -l Sent
-rw------- 1 jd jd 4275149616 Feb 5 15:56 Sent

So, Thunderbird  (17.0.2) is still broken and limited to file size of 4GB.
Long time ago, I  had opened a Mozilla/Thunderbird bug against this 
limitation,
which Thunderbird devs have closed as fixed.
Obviously it is not.
Here we are- Linux has been supporting 64bit file sizes for how many 
years now???
And yet, TB is still stuck at 4GB.