[Dovecot] Locking /var/mail/user issue with postfix and dovecot

[Robert JR]

Hello,

I have a question regarding mailbox locking and hope any one can help 
me to better understanding the locking of mbox

My Postfix lock option is fcntl dotlock
mailbox_delivery_lock = fcntl, dotlock
virtual_mailbox_lock = fcntl, dotlock

My Dovecot lock option is fcntl only
mbox_write_locks = fcntl
mbox_read_locks = fcntl


now, when user is download a large mail (20 MB) for example, dovecot 
locks
/var/mail/user with fcntl until the users finish downloading the mail

ok here comes my question.

While the user is downloading the mail , a mail arrives so postfix make 
some thing weird

1- Postfix creates /var/mail/user.lock for 5 secs , then postfix defer 
the mail with reason that the /var/mail/user is locked and then delete 
the /var/mail/user.lock (after 5 secs)

My question is ? why postfix create user.lock although it shouldn't 
because already dovecot fcntl it …

1- Dovecot locks /var/mail/user using FCNTL

2- Posttix at the same time tries to FCNTL /var/mail/user .. but it 
fail since dovecot already fcnl it.

3- Postfix at the same time add dot lock /var/mail/user for 5 secs then 
remove the lock.

the question is how come postfix dot lock /var/mail although it 
couldn't FCNTL the file in the first place ??????? what i was expecting 
is

1- Dovecot locks /var/mail/user using FCNTL

2- Postfix tries to FCNTL /var/mail/user

3- POSTFIX WILL NOT CREATE DOTLOCK file unless the FCNTL is released by
dovecot!!!!

Please advise if postfix will dot lock the file even if it couldn't 
FCNTL
the file in the first place……

Regards