==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.8
- Linux/BSD distribution name and version: CentOS Linux release 7.5.1804 (Core)
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): LDAP
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Good day. Today I installed the new version of iRedmail(First time installing 0.9.8) on clean Linux with some my changes.

Before install I changed sysctl.conf to
------------------------------

vm.overcommit_memory = 1
net.core.somaxconn = 65535
vm.dirty_expire_centisecs=60000
vm.dirty_background_ratio=80
vm.dirty_ratio=90

# Optimization for port usefor LBs
# Increase system file descriptor limit
fs.file-max = 1199971

# Allow for more PIDs (to reduce rollover problems); may break some programs 32768
kernel.pid_max = 65536

# Increase system IP port limits
net.ipv4.ip_local_port_range = 2000 65000

# Increase TCP max buffer size setable using setsockopt()
net.ipv4.tcp_rmem = 4096 87380 8388608
net.ipv4.tcp_wmem = 4096 87380 8388608

# Increase Linux auto tuning TCP buffer limits
# min, default, and max number of bytes to use
# set max to at least 4MB, or higher if you use very high BDP paths
# Tcp Windows etc
net.core.rmem_max = 8388608
net.core.wmem_max = 8388608
net.core.netdev_max_backlog = 5000
net.ipv4.tcp_window_scaling = 1

#IPV6
net.ipv6.conf.all.disable_ipv6 = 1
------------------------------

I am doing this always, and did before on many mail servers where I installed iRedmail, but this time its changed to:

-----------------------------------------------
vm.overcommit_memory =90
net.core.somaxconn =90
vm.dirty_expire_centisecs=90
vm.dirty_background_ratio=90
vm.dirty_ratio=90

# Optimization for port usefor LBs
# Increase system file descriptor limit
fs.file-max =90

# Allow for more PIDs (to reduce rollover problems); may break some programs 32768
kernel.pid_max =90

# Increase system IP port limits
net.ipv4.ip_local_port_range =90

# Increase TCP max buffer size setable using setsockopt()
net.ipv4.tcp_rmem =90
net.ipv4.tcp_wmem =90

# Increase Linux auto tuning TCP buffer limits
# min, default, and max number of bytes to use
# set max to at least 4MB, or higher if you use very high BDP paths
# Tcp Windows etc
net.core.rmem_max =90
net.core.wmem_max =90
net.core.netdev_max_backlog =90
net.ipv4.tcp_window_scaling =90

#IPV6
net.ipv6.conf.all.disable_ipv6 =90

-------------------------------------------------------

End of course it couse many problems, please fix it, if you need on install make some changes, do it directly, not on all parameters there.