Look under Tools/Account Settings, Synchronization & Storage for the account, in the Disk Space section: 'Don't download messages greater than'.

I tried to find this BUT there is NO such space in the disc section to do this

Synchronization & Storage is for IMAP accounts. For POP accounts, the corresponding section in Account Settings is Disk Space.

Still unable to do anything about download size

The same this morning all are TRUNCATED tried to fix still the same

• Menu icon > Options > Options > Advanced > 'General' tab
• click on 'Config Editor' button
• In top search type: limit_offline

look for this line:

• mail.server.default.limit_offline_message_size;

If the Value says 'True':

• double click on that line to change it to 'False'

If you see a line that looks like:

• mail.server.server3.limit_offline_message_size

note the server number may be different

If the Value says 'True':

• double click on that line to change it to 'False'

• close the window - top right X
• click on 'OK'

Report back on whether you needed to change anything back to false.

Then restart Thunderbird and check those values to see if anything has reverted back.

Also: Do you use anything like CCLeaner or an Anti-virus program which is set to clean up files ?