ExchangeClient address for IONOS

Can you tell me what the ExchangeClient address should be for IONOS Exchange 2019.
Normal address is

Hi David,

Try this:

var exchange = new ExchangeClient("");

Does this work for you?


Unfortunately not - I am still getting a server error when I try to get a list of messages


    ' Create a new Exchange client.
    Dim exchangeClient = New ExchangeClient("")

    exchangeClient.Authenticate("Username", "Password")

    ' List the first ten messages in the Inbox folder.
    Dim messageInfos = exchangeClient.ListMessages("Inbox", 0, 10)

Any ideas?

What is the error message that you get?
Is it perhaps:

Unauthorized - invalid domain or login credentials.

I’m not sure, but I presume that you’ll need to use a different password (like an app password) instead of your account. Have you tried contacting the support?

I was unable to find any documentation from them regarding the EWS.
I found only for SMTP, POP, and IMAP:


The error message is:

WebException: The remote server returned an error: (500) Internal Server Error.

I have tried IONOS support but they simply confirmed that this is the correct address. The User name and password is definitely correct.

Thanks for your support with this.

I’m getting a 401 error, not a 500.
Please send us a small Visual Studio project that reproduces your issue so we can investigate it.

I am using the example code you provided for (just changing server details)

Error occurs at: Dim messageInfos = exchangeClient.ListMessages("Inbox", 0, 10)

Imports System
Imports GemBox.Email
Imports GemBox.Email.Exchange

Module Program

    Sub Main()

        ' If using the Professional version, put your serial key below.

        ' Create a new Exchange client.
        Dim exchangeClient = new ExchangeClient("")
        exchangeClient.Authenticate("<USERNAME>", "<PASSWORD>")

        ' List the first ten messages in the Inbox folder.
        Dim messageInfos = exchangeClient.ListMessages("Inbox", 0, 10)

        For Each messageInfo As ExchangeMessageInfo in messageInfos
            If Not messageInfo.IsRead Then
                ' Get the full mail message.
                Dim mailMessage = exchangeClient.GetMessage(messageInfo.ExchangeMessageId)
                Console.WriteLine("From: " + string.Join(", ", mailMessage.From))

                ' Mark message as read.
            End If

    End Sub
End Module

I’m guessing that the problem could be with the TLS, for example, if your application is targeting an older .NET Framework then it won’t use TLS 1.2 by default.

This is why the repro project would be very helpful, we could investigate your exact issue and try to resolve it.

So again, please send us a small project that we can run on our end, you can send it to us via email or support ticket, see the Contact page.

Happy to send you the code but I don’t seem to be able to send you a ZIP file. I can confirm that the app is targeting NET version 4.7.1


Nevertheless, perhaps you could upload it somewhere temporarily and then send us a download link (again, send it to our email or create a support ticket).

Not sure - shows an error when you try to upload a Zip file.

You can download it from

I tried running your project, I got this error:

Unauthorized - invalid domain or login credentials.

This issue was resolved in the following bugfix version for GemBox.Email:

Install-Package GemBox.Email -Version 17.0.1184-hotfix