==== Required information ====
- iRedMail version (check /etc/iredmail-release):     v0.9.4
- Linux/BSD distribution name and version: centos 6.4
- 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:

Jun 25 09:45:55 imap-login: Info: Login: user=<miaobai1101@88ipa.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, mpid=15450, secured, session=<yB60chA2igB/AAAB>
Jun 25 09:45:55 imap(miaobai1101@88ipa.com): Error: user miaobai1101@88ipa.com: Initialization failed: Namespace '': mkdir(/var/vmail/vmail1/88ipa.com/m/i/a/miaobai1101-2016.5.25.7.30.33//Maildir) failed: No space left on device
Jun 25 09:45:55 imap(miaobai1101@88ipa.com): Error: Invalid user settings. Refer to server log for more information.

[root@server03 vmail1]# df -lh
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        50G   17G   31G  36% /
tmpfs           939M     0  939M   0% /dev/shm

[root@server03 vmail1]# df -i
Filesystem      Inodes   IUsed  IFree IUse% Mounted on
/dev/vda1      3276800 3276800      0  100% /
tmpfs           240302       1 240301    1% /dev/shm

====
我使用df -lh 命令查看硬盘剩余空间，还有60%多，肯定够用的，再用df -i 查看了Inodes使用情况，满了。目前应该有10几万账号，怎么解决?