For the current design of Notes Client when sending a mail and one of the recipients is not found in a directory the user is displayed a 'no match' dialog that offers possible suggestions for the user. The user has the options to select a name and hit OK , send anyway , skip name , skip all or cancel send.
When the sender choose "OK" or "Send anyway", the mail will be delivered to the first user from the list. This current design is not secured and confidential information might be delivered to the incorrect recipient/user. Hence requesting for an enhancement to remove the "No Match" dialog when recipient is from an external domain.