Issue with SendMessage API – "Index was outside the bounds of the array."

Problem reported by yerim kim - 8/26/2025 at 6:37 PM

Submitted

Hello,

I am currently evaluating SmarterMail with the Free license before moving forward with a purchase.

As part of the testing, I am developing an API integration for sending and receiving mail. Receiving works without issues, but I am running into a problem when sending mail using the SendMessage API.

Environment: ASP.NET C#

The problem is that regardless of which parameters I include in the request, the API always responds with:

"Index was outside the bounds of the array."

Here is the request I am making:

var mailData = new
{
    to = "\"test@receive.com\" <test@receive.com>;",
    ownerEmailAddress = "send@test.com",
    from = "send@test.com",
    subject = "test",
    messageHTML = "test"
};

I have checked the community forum, but I have not been able to find a post that addresses this specific error.

Could you please advise what might be causing this?

Is there an issue with the request payload format?
Or is there a domain/mailbox configuration setting in SmarterMail that I need to adjust?

The API documentation does not provide enough information for me to determine the cause. Any guidance or suggestions would be greatly appreciated.

Thank you.

4 Replies

Reply to Thread

Zach Sylvester Replied

8/26/2025 at 7:45 PM

Employee Post

Try setting the To like this

to = "test@receive.com"

Let me know if this helps.

Zach Sylvester

Software Developer
SmarterTools Inc.

www.smartertools.com

yerim kim Replied

8/26/2025 at 11:22 PM

Thank you for your response. However, I am still encountering the same error.

Just in case it helps, I am also attaching the HTTP request code below.

Here is the code I am using to make the request.

using (var client = new HttpClient())
                {
                    var mailData = new
                    {
                        to = "test@receive.com",
                        ownerEmailAddress = "send@test.com",
                        from = "send@test.com",
                        subject = "test",
                        messageHTML = "test"
                    };

                    var json = JsonConvert.SerializeObject(mailData);
                    var content = new StringContent(json, Encoding.UTF8, "application/json");
                    client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", token);

                    var response = client.PostAsync(uri, content).Result;
                    dynamic result = JsonConvert.DeserializeObject(response.Content.ReadAsStringAsync().Result);

                    if (!response.IsSuccessStatusCode)
                    {
                        throw new Exception($"Sending message failed with status code {response.StatusCode} / {result.message}");
                    }

                    return result;
                }

Index was outside the bounds of the array. -> This error message is coming from the value of result.message in the response.