[gentoo-user] local mail access - Lock file

I have access to local mail via "mutt" (which I don't use very often
nowadays) so in order to access local "mbox" from Thunderbird I had to
create an account (via Add Other Accounts) from Thunderbird settings.
Is it the way to do it?

Can I just create in my local folder /home/thelma/.thunderbird
a link to /var/spool/mail ?

Anyhow, when I added local account: thelma@localhost I could see all the
local mail but when I deleted them (mostly cron job mails) they all came
back.

How these programs decide which one own a Lock.file?

-- 
Thelma