==== Required information ====
- iRedMail version (check /etc/iredmail-release):
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
======== Required information ====
- iRedMail version (check /etc/iredmail-release): iRedMail-0.9.2.tar.bz2
- Linux/BSD distribution name and version: ubuntu
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- Related log if you're reporting an issue:
====

I have followed the installation instructions of iRedMail and it's installed with no error. Everything's running well such as iRedAdmin, RoundCube. However, when I send an e-mail, it sends, but after the first e-mail, it starts not to send. And sometimes it receives mails. When I reboot server, again it sends first e-mail but after neither sends nor receives. I couldn't solve the unstable situation. What should I do?

I had tried different VPS,such as Crissic.net and digitalocean,but all same this problem.

At the beginning,I thought my DNS is unstable,but I replaced DNS server,same problem too.

Many thanks!