We run a newsletter subscription service from our website. The newsletters emails always get caught in quarantine, by our Symantec Email Security Service. When external email addresses (like my Yahoo email address) receive our newsletter, the sender address is always the same (similar to firstname.lastname@example.org), but when our internal email users receive the newsletter, the sender email address is randomly generated and does not have our company email domain (like email@example.com and firstname.lastname@example.org).
We are unable to whitelist any of the sender email addresses for our internal email users. Any suggestions will be appreciated.