Authentication with LeadMailbox is very simple. When the connector is installed you will need to provide the name of your account only.
Post Leads method
When you call the Post Leads method, you need to provide the name of the Campaign you want to add the Lead to.
You can find these values from the LeadMailbox dashboard:
The Name of your Campaign]
Show Post Url
This shows the values you can use for both the Account Name and the Campaign Name.