Sometimes can not get emails from customers. They send us even twice but nothing. For example today, our account guntis@autorepublika.lv didnt received some emails. 

28 april we had following issue and customer reported.

>This is the mail system at host  mail.privatbank.lv .
>
>I'm sorry to have to inform you that your message could not
>be delivered to one or more recipients. It's attached below.
>
>For further assistance, please send mail to postmaster.
>
>If you do so, please include this problem report. You can
>delete your own text from the attached returned message.
>
>                   The mail system
>
>< guntis@autorepublika.lv >: host  mx.zoho.com [74.201.154.201] said: 554
>Security
>    violation. Email Session ID: {553F8022-1A-CFEA8C0-C0000001} (in reply
>to
>    end of DATA command)