==== 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:
====I have installed iRedMail on fresh OS. However I encounter problem now, I cannot receive mail from outside. I can receive mail from my own created domain, but when I tried to send email from other domain such as gmail, I cannot receive it.

I tried command:
sendmail -bp

result:
C661BC09B85A     3372 Sat Aug 27 19:19:24  xxx@gmail.com
                                                  (mail transport unavailable)
                                         test@xxx.com

The log file on /var/mail/maillog entry is below:
Aug 27 19:55:19 localhost postfix/postscreen[10425]: CONNECT from [209.85.218.43]:35630 to [192.168.3.52]:25
Aug 27 19:55:25 localhost postfix/postscreen[10425]: PASS NEW [209.85.218.43]:35630
Aug 27 19:55:25 localhost postfix/smtpd[10431]: connect from mail-oi0-f43.google.com[209.85.218.43]
Aug 27 19:55:26 localhost postfix/smtpd[10431]: Anonymous TLS connection established from mail-oi0-f43.google.com[209.85.218.43]: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
Aug 27 19:55:27 localhost postfix/smtpd[10431]: 396ABC09B84A: client=mail-oi0-f43.google.com[209.85.218.43]
Aug 27 19:55:27 localhost postfix/cleanup[10444]: 396ABC09B84A: message-id=<CAOiTqEw2w0XQoAvEaWOOQo=d-P2=No8qv8a+=tYt9EFs0_MXSA@mail.gmail.com>
Aug 27 19:55:27 localhost postfix/qmgr[2806]: 396ABC09B84A: from=<xxx@gmail.com>, size=3472, nrcpt=1 (queue active)
Aug 27 19:55:27 localhost postfix/qmgr[2806]: warning: connect to transport private/amavis: No such file or directory
Aug 27 19:55:27 localhost postfix/error[10449]: 396ABC09B84A: to=<test@xxx.com>, relay=none, delay=0.63, delays=0.58/0.01/0/0.04, dsn=4.3.0, status=deferred (mail transport unavailable)
Aug 27 19:55:27 localhost postfix/smtpd[10431]: disconnect from mail-oi0-f43.google.com[209.85.218.43]

Can anyone give me hint of what should I try next as I'm very new to this.

Thank you.

==== Required information ====
- iRedMail version (check /etc/iredmail-release): 0.9.5-1
- Linux/BSD distribution name and version: CENTOS 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): PGSQL
- Web server (Apache or Nginx): Apache
- Manage mail accounts with iRedAdmin-Pro? No
- Related log if you're reporting an issue:
====