[mew-int 2852] How can I delete invalid messages safely?

Hi guys ;-)

Gmail is my daily email service provider. I have still subscribed the
'All mail', so after reading the messages in the '%inbox', I can refile
them to '%[Gmail]/All mail' just like 'Archive' in Gmail's web page.

But there will still be invalid messages in the '%[Gmail]/All mail' 
after doing the operation above. And there will be more and more messages
in the folder. I just wanna 'Archive' them to the Gmail IMAP server and
I do not want to see and need them off-line.

According the info, it talks about deleting invalid message off-line.
I can't figure out whether the `s' operation is safe or not. Most of 
the time I use Mew online and refile the messages in '%inbox' by `o' & `x'
not `lx'.

Can I just remove the messages files in the directory like 
'~/Mail/#imap/[email protected]@imap.gmail.com#imap/[Gmail]/All Mail'

or is there any way to not show the invalid messages in '%[Gmail]/All Mail'
and keep my refiled messages safely in the IMAP server?

Best regard!