While using a MAPI email plugin with Windows Vista/7+, the default email client (Outlook, Windows Mail, etc.) will not preview the message. An “Unknown Error” or “User Abort” error is returned in most cases.
1. In order for MAPI to function correctly, the bitness of the MAPI application (Delphi/RB application) must match the bitness of the client email application (Outlook). For instance, a 32 bit Delphi application is only compatible with a 32 bit installation of the email client.
In order to resolve this, a 32 bit email client must be installed for all 32 bit Delphi/RB applications or a 64 bit Delphi/RB application must be provided for machines with 64 bit email client installations. Outlook currently provides installations for 32 bit and 64 bit and it is possible to install Outlook 32 bit on a 64 bit machine. Delphi XE2 or higher is required for 64 bit compilation. See the following Microsoft article for more information.
2. This issue may be due to access rights differences between the host application and the email client. If for instance you are running Delphi in Administrator mode and have Outlook running in User mode, you will receive an error. To solve the problem, simply be sure each application is running under the same security context.