Outlook 365插件无法获取Exchange邮件发件人SMTP地址问题

我们正在开发一款Outlook 365插件，需要提取邮件信息生成文件，但收件箱中通过Exchange发送的邮件始终无法获取发件人信息。采用微软官方文档中的方法实现后，代码始终返回null。

原实现代码 #

private string GetSenderSMTPAddress(Microsoft.Office.Interop.Outlook.MailItem mail)
{
    string PR_SMTP_ADDRESS =
        @"http://schemas.microsoft.com/mapi/proptag/0x39FE001E";
    if (mail == null)
    {
        throw new ArgumentNullException();
    }
    if (mail.SenderEmailType == "EX")
    {
        Microsoft.Office.Interop.Outlook.AddressEntry sender =
            mail.Sender;
        if (sender != null)
        {
            //Now we have an AddressEntry representing the Sender
            if (sender.AddressEntryUserType ==
                Microsoft.Office.Interop.Outlook.OlAddressEntryUserType.
                olExchangeUserAddressEntry
                || sender.AddressEntryUserType ==
                Microsoft.Office.Interop.Outlook.OlAddressEntryUserType.
                olExchangeRemoteUserAddressEntry)
            {
                //Use the ExchangeUser object PrimarySMTPAddress
                Microsoft.Office.Interop.Outlook.ExchangeUser exchUser =
                    sender.GetExchangeUser();
                if (exchUser != null)
                {
                    return exchUser.PrimarySmtpAddress;
                }
                else
                {
                    return null;
                }
            }
            else
            {
                return sender.PropertyAccessor.GetProperty(
                    PR_SMTP_ADDRESS) as string;
            }
        }
        else
        {
            return null;
        }
    }
    else
    {
        return mail.SenderEmailAddress;
    }
}

当前问题点 #

代码在以下环节返回null：获取到ExchangeUser对象后，访问其PrimarySmtpAddress属性时无有效返回：

if (exchUser != null)
{
    return exchUser.PrimarySmtpAddress;
}

解决方案 #

1. 优先通过PropertyAccessor读取MAPI属性 #

跳过ExchangeUser对象的依赖，直接读取PR_SMTP_ADDRESS属性，即使是Exchange类型的地址条目也能兼容。修改后的代码如下：

private string GetSenderSMTPAddress(Microsoft.Office.Interop.Outlook.MailItem mail)
{
    const string PR_SMTP_ADDRESS = @"http://schemas.microsoft.com/mapi/proptag/0x39FE001E";
    if (mail == null)
        throw new ArgumentNullException(nameof(mail));

    if (mail.SenderEmailType == "EX")
    {
        var sender = mail.Sender;
        if (sender != null)
        {
            try
            {
                // 直接读取SMTP地址属性
                return sender.PropertyAccessor.GetProperty(PR_SMTP_ADDRESS) as string;
            }
            catch (Exception)
            {
                // 读取失败时回退到原逻辑
                if (sender.AddressEntryUserType == Microsoft.Office.Interop.Outlook.OlAddressEntryUserType.olExchangeUserAddressEntry ||
                    sender.AddressEntryUserType == Microsoft.Office.Interop.Outlook.OlAddressEntryUserType.olExchangeRemoteUserAddressEntry)
                {
                    var exchUser = sender.GetExchangeUser();
                    return exchUser?.PrimarySmtpAddress;
                }
                return null;
            }
        }
        return null;
    }
    else
    {
        return mail.SenderEmailAddress;
    }
}

2. 尝试读取备用MAPI属性 #

如果PR_SMTP_ADDRESS读取失败，可以尝试读取PR_SENDER_EMAIL_ADDRESS属性（标签为0x0C1F001E），替换对应读取逻辑即可：

const string PR_SENDER_EMAIL_ADDRESS = @"http://schemas.microsoft.com/mapi/proptag/0x0C1F001E";
// 在代码中使用
return sender.PropertyAccessor.GetProperty(PR_SENDER_EMAIL_ADDRESS) as string;

3. 检查权限与配置 #

• 确保插件拥有足够权限访问Exchange用户信息，尤其是跨租户或外部Exchange用户场景。
• 确认Exchange服务器地址簿配置允许客户端获取用户SMTP地址。

内容的提问来源于stack exchange，提问作者velteyn