Again, thank you for your kind attention Sir.
I run these commands but couldn´t obtain the user with permission over this files.
I run:

lsof | grep "/maildir/domain.com/user/.Sent/cur/mail_id"

lsof "/maildir/domain.com/user/.Sent/cur/mail_id" (THIS LINE WITHOUT THE GREP FILTER)

lsof | grep /maildir/domain.com/user/.Sent/cur/mail_id (THIS LINE WIYHOUT QUOTES)

lsof /maildir/domain.com/user/.Sent/cur/mail_id (THIS LINE WITHOUT THE GREP FILTER AND WITHOU QUOTES)

But dont´t tell me anything about the user who is owning this file, although I´m logged as root in the system.
Thanks for your patience and your help Sir.

Thanks again mfillpot for taking time to answer me.
Could you please give me an example of how would you combine the lsof with the grep command so as to be able to find those files in the mail directory?
Thank you very much Sir.

This is what I find with lsof:

lsof -i :143
COMMAND PID USER FD TYPE DEVICE SIZE NODE NAME
couriertc 2849 root 3u IPv4 7630 TCP mail.server:imap2 (LISTEN)
couriertc 2849 root 5u IPv4 7631 TCP localhost:imap2 (LISTEN)

Seems that root is the username being used.
I´ve changed the courier directory UID and GID to mail:mail but when I do lsof -i :143 still root as the username in used.
Still can´t find a solution to this issue.
Thanks again for you attention.

Thank you very much for your help mfillpot.
I´ll be testing what I can find with lsof and post what I find.
Thanks again.

Best regards

Hi Dear Sirs:
I am having a little problem with permissions of a file, and can´t find a solution,
I have a mail Server with Postfix, Courier and Roundcube as Webmail.
When I give in the user´s directory permissions to root (/maildir/user root:root), login is ok in Roundcube but can´t send mails, and logs show: "/maildir/domain.com/user/tmp/mail_id.server_name: Permission denied)"
If I give in user´s directory permissions to another user, for example mail (/maildir/user mail:mail), I can send mails but can´t login into Roundcube Webmail.
Please excuse me if this is not the correct place for asking for help with this issue.
But I ´ve been looking for a solution for some days but can´t find it.
Any help will be welcome.
Thanks for your attention Sirs.
Best regards,

Javier