Private email domains tend to have more aggressive firewalls and spam filters than Gmail or other free webmail providers. Sometimes, these network firewalls and filters can block your campaigns.
If subscribers from a certain company or private email domain have trouble receiving your Clever Elements campaigns, ask them to whitelist Clever Elements as a possible solution.
Delivery Domains and Addresses
*@*.newscpt1.de + *@newscpt1.de
*@*.newscpt2.de + *@newscpt2.de
… bis ...
*@*.newscpt24.de + *@newscpt24.de