When to release COM objects?

var application = (Application)ADXAddinModule.CurrentInstance.HostApplication;
var mailItem = (MailItem) application.CreateItem(OlItemType.olMailItem);
mailItem.Attachments.Add("Path...");

Application application = (Application)ADXAddinModule.CurrentInstance.HostApplication;
Inspector inspector = application.ActiveInspector();
Document document = inspector.WordEditor as Document;
Windows windows = document.Windows;
Window window = windows[1];
Microsoft.Office.Interop.Word.Selection selection = window.Selection;
selection.InsertAfter("Text");

Application application = (Application)ADXAddinModule.CurrentInstance.HostApplication;
NameSpace session = application.Session;
Accounts accounts = session.Accounts;
foreach (var account in accounts)
{                
}

Marshal.IsComObject(myObject)

Marshal.IsComObject(myObject)

var person = this.GetPerson();
var address = person.Address; //Address is a struct, not a class
address.Street = "New Address";

person.Address.Street = "New Street";

var person = this.GetPerson();
var address = person.Address;
address.Street = "New Street";
person.Address = address;

public MailItem GetSelectedMail()
{
    Application application = null;
    Explorer activeExplorer = null;
    Selection selection = null;

    try
    {
        application = ADXAddinModule.CurrentInstance.HostApplication as Application;

        if (application != null)
        {
            activeExplorer = application.ActiveExplorer();

            if (activeExplorer != null)
            {
                selection = activeExplorer.Selection;
                if (selection.Count > 0 && selection.Class == OlObjectClass.olMail)
                {
                    return selection[1] as MailItem;
                }
            }

            return null;
        }
    }
    finally
    {
        if (selection != null)
            Marshal.ReleaseComObject(selection);

        if (activeExplorer != null)
            Marshal.ReleaseComObject(activeExplorer);

        if (application != null)
            Marshal.ReleaseComObject(application);
    }
}

AddinModule.CurrentInstance.OutlookApp

mailItem.Attachments.Add("Path...");

public static class XL
{
    public static Excel._Application App
    {
        get { return AddinModule.CurrentInstance.ExcelApp; }
    }

    public static int Version
    {
        get { return AddinModule.CurrentInstance.HostMajorVersion; }
    }
}

public class ComReference<T> : IDisposable
{
    private static readonly Logger logger;

    static ComReference()
    {
        logger = LogManager.GetLogger("ComReference");
    }

    private readonly T reference;

    private Boolean isDisposed;

    public T Reference
    {
        get { return this.reference; }
    }

    public ComReference(T reference)
    {
        if (logger.IsEnabled(LogLevel.Trace))
            logger.Log(LogLevel.Trace, "Creating");

        this.reference = reference;
    }

    ~ComReference()
    {
        if (!this.isDisposed)
        {
            if (logger.IsEnabled(LogLevel.Warn))
                logger.Log(LogLevel.Warn, "This instance of ComReference<{0}> is finialized before Dispose() was called.", typeof(T).FullName);
        }
    }

    public void Dispose()
    {
        if (this.isDisposed)
        {
            throw new InvalidOperationException(Stri ng.Format("This instance of ComReference<{0}> is already disposed.", typeof(T).FullName));
        }

        if (this.reference != null && Marshal.IsComObject(this.reference))
        {
            Marshal.ReleaseComObject(this.reference);
        }

        this.isDisposed = true;
    }
}

using (var mailItemReference = new ComReference<MailItem>(mailItem))
{
    mailItemReference.Reference.Subject = "Test";
}