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