C# Exchange EmailMessage Send: As soon as I add an attachement, I get error "No mailbox with su-CodePudding

In my application I use some code to send automated mails over our Exchange server.

My current goal is to send a HTML mail with some pictures as a handout. That pictures shall be attachments of the mail.

To this point the code is working (I have changes internal names in the code example):

ExchangeService MailClient = new ExchangeService
{
    UseDefaultCredentials = true,
    Url = new Uri("https://<domain.of.company>/EWS/Exchange.asmx")
};

EmailMessage msg = new EmailMessage(MailClient);

msg.ToRecipients.Add(new EmailAddress(user.EmailAddress));

msg.Sender = new EmailAddress("[email protected]");

msg.Subject = "Some text here";

MessageBody Body = new MessageBody
{
    BodyType = BodyType.HTML,
    Text = NameOfApplication.Properties.Resources.Embedded_HTML_File
};

msg.Body = Body;

msg.SendAndSaveCopy(new FolderId(WellKnownFolderName.SentItems, "[email protected]")));

With this code the E-Mail get saved in the "Sent" folder and arrives the target mailbox. Success so far.

But as soon I add an attachement by this (no other changes were made)

msg.Attachments.AddFileAttachment(AppContext.BaseDirectory   "Logo.jpg");

SendAndSaveCopy throws an exception with the description "No mailbox with such guid."

When I comment out the AddFileAttachment line the code is working again.

Any idea whats wrong with attachments?

CodePudding user response：

Found the solution. Reading tooltips might help.

Maybe the day will come, when Microsoft will change SendAndSaveCopy to include this step.

But yes: The error message is misleading.