8.0.3-103395 GW Server on SLES 10 SP3
8.0.3-108711 GW Client von WinXP SP3
The issue is related to just one useraccount, no matter if in caching or online mode and it appeared suddenly without a known change to the systems.
Changed GW client Version, hostsystem, GW mode, other accounts got no issues with the affected recipient.
GWchecks to fix structure + index / contents of the accounts have been completed without any improvement.

Addressing a specific external email recipient per "cc" creates a wrong frequent contacts entry. If addressing the recipient per "to" field, everything works fine. The tooltip shows the correct email address when moving over in the cc field but the email will be send to the wrong address.

The recipients email address looks like this: forename.surname@company-appartment.tld
The frequent contacts entry looks like this: forename.surname.foo_PO.bar_DOM@company-appartment.tld

If the contact's email address got corrected, the wrong contact gets created again after sending any further email with the recipient per "cc".

How does a internal postoffice/domain name gets mixed up into an external email address?