public async Task<PostmarkCompleteSenderSignature> CreateSignatureAsync(string fromEmail, string name, string replyToEmail = null, string returnPathDomain = null)
{
var parameters = new Dictionary<string, object>();
parameters["FromEmail"] = fromEmail;
parameters["Name"] = name;
parameters["ReplyToEmail"] = replyToEmail;
parameters["ReturnPathDomain"] = returnPathDomain;
return await this.ProcessRequestAsync<Dictionary<string, object>, PostmarkCompleteSenderSignature>
("/senders/", HttpMethod.Post, parameters);
}