MessageClient constructor
Initialise a MessageClient instance.
Parameters:
client- the http client to use for sending requests.domain- the domain of the Mailgun account.apiKey- the API key of the Mailgun account.host- the host to send requests to.callback- a callback function that is called after the request is sent.
Implementation
MessageClient(super.client, super.domain, super.apiKey, super.host,
[super.callback]);