Emails from my domain blocks by the Symantec antispam filter

Greetings

I'm a system administrator in the company Sirius Extrusion. My company has clients that use your antispam filter. Unfortunately your antispam filter has started to block our emails without any reason.  My colleagues receives "553 Message filtered" response. Our domain isn't in any spam database, it has SPF record and our email server isn't open relay.

Could you please stop to block our emails and add our domain to the your whitelist?

Our domain: sirius.pro

Thanks.

P.S. I can provide more detailed information about us if it will be necessary.