Spec:
{
    smtp : {
        server: string, (without port)
        username : string,
        password : string
    },
    to: [{
        name?: string,
        address: string
    }],
    from: {
        name?: string,
        address: string
    },
    reply_to?: {
        name?: string,
        address: string
    },
    subject: string,
    message: {
        mime: string,
        content: string
    }
}