How can I set file permissions for new files in Maildir?

So I run debian 10 through VMbox on win10. I am setting up an email server right now and the things that won’t let me turn in this quest is that I can’t receive mail from the internet though I can send it. The mail is stored in /var/mail/Maildir and subfolders like new, cur, tmp and when an email drops in, this file doesn’t have the right permissions and I can’t read it through thunderbird until I manually set the rights. All the new letters have -rw——-+ permissions. What can I do to make all new letters have 755 rights automatically? I really need help, I am still new to this and not being able to figure it out drives me mad.

Things I’ve tried:

chown -R :mail /var/mail/Maildir
chmod -R 755 /var/mail/Maildir

and

setfacl -R -m "group:mail:rwX" $dir                # Sets the effective ACL.
setfacl -R -d -m "group:mail:rwX" $dir             # Sets the inheritable ACL.

But still I can’t get the permissions right. I use passwd database as a driver so all the users are local debian users like root or alex united by "mail" group.

In logs I have this:

Jul 21 21:42:15 mail dovecot: imap(alex)<2920><4nRq+/eqcMl/AAAB>: Error: Mailbox INBOX: open(/var/mail/Maildir/cur/1595355455.Vfe04Idf939M195657.mail.magrega.ru.eu.org:2,) failed: Permission denied (euid=1003(alex) egid=1004(alex) missing +r perm: /var/mail/Maildir/cur/1595355455.Vfe04Idf939M195657.mail.magrega.ru.eu.org:2,)
Jul 21 21:42:15 mail dovecot: imap(alex)<2920><4nRq+/eqcMl/AAAB>: FETCH failed: Internal error occurred. Refer to server log for more information. [2020-07-21 21:42:15] in=275 out=1023 deleted=0 expunged=0 trashed=0 hdr_count=0 hdr_bytes=0 body_count=0 body_bytes=0

I enter chmod g+r var/mail/Maildir/cur/ and everything starts working until I get a new mail which has only -rw------+ permissions.