Postfix/Dovecot/MySQL configuration and troubleshooting

I try to configure Postfix, Dovecot and mysql following this tutorial https://www.linode.com/docs/email/postf … -and-mysql">https://www.linode.com/docs/email/postfix/email-with-postfix-dovecot-and-mysql

the configuration was successful any error or log warnings. But I can't configure a account on client mail, when I try that in gmail for example I have this error message:
> Connection timed out: There may be a problem with the settings you added. Please contact your other email provider to verify the correct server name and port.

Only this appears on the log:

Aug 12 23:08:31 localhost postfix/smtpd[7427]: disconnect from bpe-exc-hub-01.dualtec.com.br[187.95.198.220]
Aug 12 23:11:51 localhost postfix/anvil[7429]: statistics: max connection rate 1/60s for (smtp:187.95.198.220) at Aug 12 20:08:29
Aug 12 23:11:51 localhost postfix/anvil[7429]: statistics: max connection count 1 for (smtp:187.95.198.220) at Aug 12 20:08:29
Aug 12 23:11:51 localhost postfix/anvil[7429]: statistics: max cache size 1 at Aug 12 20:08:29

I try to troubleshooting whit this guide https://www.linode.com/docs/email/postf … -and-mysql">https://www.linode.com/docs/email/postfix/troubleshooting-problems-with-postfix-dovecot-and-mysql

But my problem persist.

someone can help with commons problems or some tests this?