EWS Managed API：能否为邮件分配外部GUID用于后续搜索？

Absolutely, you can assign a custom GUID/identifier to an EmailMessage for later search purposes—here's a practical breakdown of how to make this work, aligned with your example code:

1. Store the GUID in the Email Object #

First, you need a way to attach the GUID to your email. How you do this depends on whether you're using a custom EmailMessage class or a third-party library:

• If you've built your own EmailMessage wrapper (like your example shows), simply add an ExternalGuid property (type Guid or string) to the class.
• If using a standard email library (e.g., MailKit, Exchange Web Services), use a custom email header (like X-External-Guid) to store the GUID. This ensures the identifier travels with the email and gets saved on the server.

2. Assign the GUID & Send the Email #

Custom Wrapper Class Scenario #

This matches the code structure you provided. You'll want to persist a mapping between the GUID and the email's system-generated ID (for easy later lookup):

// Generate a unique GUID
var externalGuid = Guid.NewGuid();

// Initialize your email and assign the GUID
var email = new EmailMessage(_service);
email.ExternalGuid = externalGuid;

// Send the email, then save the GUID-to-email mapping (e.g., in a database)
_service.Send(email);
_service.SaveEmailMapping(externalGuid, email.SystemId); // Custom method to store the relationship

Third-Party Library Scenario (e.g., MailKit) #

Use a custom header to embed the GUID directly in the email:

var externalGuid = Guid.NewGuid();
var message = new MimeMessage();

// Add custom header with your GUID
message.Headers.Add("X-External-Guid", externalGuid.ToString());

// Send the email as usual
using (var client = new SmtpClient())
{
    await client.ConnectAsync("smtp.yourdomain.com", 587, SecureSocketOptions.StartTls);
    await client.AuthenticateAsync("your-email@domain.com", "your-password");
    await client.SendAsync(message);
    await client.DisconnectAsync(true);
}

3. Check If the Email Exists Using the GUID #

Custom Wrapper + Database Mapping #

Query your stored mapping to verify existence:

public bool IsExistByExternalGuid(Guid externalGuid)
{
    // Check if the GUID exists in your mapping table
    return _dbContext.EmailMappings.Any(mapping => mapping.ExternalGuid == externalGuid);
}

Third-Party Library + Custom Header #

Search the email server for messages containing your custom header:

// Example using Exchange Web Services (EWS)
public bool IsExistByExternalGuid(Guid externalGuid)
{
    // Create a filter to search for the custom header
    var headerFilter = new SearchFilter.ContainsSubstring(
        ItemSchema.InternetMessageHeaders, 
        $"X-External-Guid: {externalGuid}"
    );

    // Search the Sent Items folder (adjust folder as needed)
    var searchResults = _service.FindItems(WellKnownFolderName.SentItems, headerFilter, new ItemView(1));
    
    // Return true if any matching email is found
    return searchResults.TotalCount > 0;
}

Key Notes #

• Ensure uniqueness: Always generate GUIDs with Guid.NewGuid() to avoid collisions.
• Flexible type: If sharing the GUID across systems, use a string representation to avoid type conversion issues.
• Server compatibility: Most mainstream email servers support custom headers, but double-check if you're using a niche service.

内容的提问来源于stack exchange，提问作者eocron