Hi - Thanks for sharing your requirements. I have gone through the attachments shared by you and found it to be perfectly matched with my skillsets.
If I understand correctly, then you want to have an option in your WinForms application to verify the address entered into the system. Once the address information is entered, it will be validated with the help of AccuMail API which will return the correct address in case there is any wrong information supplied.
Since you already have the functional application, therefore, I am assuming that only API integration is required. This API will be called before saving the data into your database so that only correct information is saved to the database. I would also suggest using the BulkCopy in order to save the data collectively to the database.
Let me know if this sounds similar to what you intend to achieve.
I shall look forward to hearing from you.
Regards,
Anil