The adapter "SQL" raised an error message. Streaming not supported over multiple column result

I get the following error with my SQL send/receive port.

The adapter "SQL" raised an error message.Streaming not supported over multiple column result.

 I don't know if this error is related to the way I have built my stored proc? This is it anyway:

 PROCEDURE [dbo].[sp_SendEmail]
 @EmailID as int,
 @EmailTo as nvarchar(50),
 @EmailFrom as nvarchar(50),
 @EmailContent as nvarchar(250)
 
AS
BEGIN

 DECLARE @mailitem_id int

 EXEC msdb.dbo.sp_send_dbmail
   @subject = @EmailSubject,
   @profile_name = 'myProfile',
   @recipients = @EmailTo,
   @body = @EmailContent,
   @mailitem_id=@mailitem_id OUTPUT;

 — return the mailID
 SELECT @mailitem_id as SysMailID for xml raw
 
END

Did someone have an idea of what could be the problem? Thanks for your help.