Hi Maciej,

I had the same issue when I switched dovecot backend from Cento 6 to Centos 7.

Also my configuration is similar to you, Dovecot Direcot, Dovecot backend that share Maildir via NFS on NetApp.

For local delivery of emails are you using LDA or LMTP? I'm using LDA.

Let me know.

Thanks

Hi
I have been trying resolve my problem with dovecot for a few days and I
dont have idea....

My environment is: dovecot director+5 dovecot guest

dovecot-2.2.36.4 from source
Linux 3.16.0-11-amd64
storage via nfs (NetApp)

all works fine but when I update OS from debian 8 (kernel 3.16.x) to
debian 9 (kernel 4.9.x ) sometimes I get random in logs:
Broken dovecot-uidlist

examle:
Error: Broken file
/vmail2/po/pollygraf.xxx_pg_pollygraf/Maildir/dovecot-uidlist line 88:
Invalid data:

(for random users - sometimes 10 error in day per node, some times more)

File looks ok

But if I change kernel to 3.16.x problem with "Broken file
dovecot-uidlist"  - not exists
if turn to 4.9 or 5.x - problem exists

I have storage via nfs with opions:
rw,sec=sys,noexec,noatime,tcp,hard,rsize=65536,wsize=65536,intr,nordirplus,nfsvers=3,tcp,actimeo=120
I tested with "nocto" or without "nocto" - nothing changes ......

nfs options in node:
mmap_disable = yes
mail_fsync = always

I bet the configuration is correct and I wonder why the problem occurs
with other kernels
3.x.x - ok
4.x - not ok

I check and user who have problem did not connect to another node in
this time

I dont have idea why problem exists on the kernel 4.x but not in 3.x

-- 
Alessio Cecchi
Postmaster @ http://www.qboxmail.it
https://www.linkedin.com/in/alessice