TO: field empty for CC: recipients

Dear Forum members,

I am experiencing a strange behaviour with send mail ever since I have upgraded my server and clients from version 5.0.13 to version 7.0.1. Some of the users who are copied in the cc: field will receive their copy but can’t see the name of the main recipient(s) in the To: field. Checked the knowledge base but couldn’t find any references. Maybe one of you came across something similar and can give me a hint.

Thank you very much in advance for your help.

Best regards,

Wolfgang Vondracek