Connect using gmail smtp, launch the main app using java -jar with as a parameter the absolute uri to a file, such as the one located in src/test/resources
Specify in the first field all the adresses, and in the "incompatible" field, the one that shouldn't be linked. This file has to be written using YAML.
Once it's launched, enter your gmail adress without the @gmail, and your gmail password, and a mail will be sent to all the users, sayin to whom they have to offer a gift.