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iRedAdmin-Pro on CentOS 6.7 MySQL version.

Have some mail files in a user directory.
/var/vmail/vmail1/domain_directory/user_directory/Maildir/cur/  ...files...

I'm copying an old message from another directory from previous iredmail system with different host name.
File is present. 
   Example name: 1410208269.M719178P10391.host_name.domain_name.tld,S=16238,W=16584:2,STa
Check permissions and it originally shows rwx______.
Chmod 600 of file.
Mail client (T-bird) cannot read the file.
The file message then seems to disappear without being removed. 

So, is there something iRedMail is doing to remove the file periodically and why can't e-mail client Thunderbird read the message?