Plus addressing (also known as sub-addressing) is a powerful email feature that allows users to append a '+' suffix to their username with arbitrary tags. For example:

myname+newsletters@domain.com
myname+shopping@domain.com

Despite these variations, all emails get delivered to the primary mailbox (myname@domain.com). This creates several advantages:

• Automatic email categorization without server-side rules
• Identifying sources of spam/leaks by unique tags
• Creating temporary addresses without provisioning new mailboxes

Microsoft Exchange Server has traditionally NOT supported plus addressing out-of-the-box. Unlike Sendmail and other SMTP servers, Exchange requires specific configuration:

# PowerShell command to check if plus addressing is enabled
Get-OrganizationConfig | Select-Object DisablePlusAddressInRecipients

Option 1: Transport Rule Configuration

Create a transport rule to handle plus addresses:

New-TransportRule -Name "PlusAddressRewrite" 
  -RecipientAddressMatchesPatterns '^([^+]+)\+[^@]+@domain\.com$'
  -SetHeaderMessage "X-Original-To" "HeaderValue"
  -SetEnvelopeRecipient '${1}@domain.com'

Option 2: Custom Mail Flow Processing

For more advanced scenarios, implement an Exchange agent:

public class PlusAddressAgent : SmtpReceiveAgent
{
    public PlusAddressAgent()
    {
        this.OnEndOfData += OnEndOfDataHandler;
    }

    private void OnEndOfDataHandler(ReceiveMessageEventSource source, EndOfDataEventArgs e)
    {
        var recipient = e.MailItem.Message.To[0].Address;
        if (recipient.Contains("+"))
        {
            var baseAddress = recipient.Substring(0, recipient.IndexOf("+")) + "@domain.com";
            e.MailItem.Message.To.Clear();
            e.MailItem.Message.To.Add(new MailAddress(baseAddress));
        }
    }
}

If native Exchange configuration isn't feasible, consider these workarounds:

• Configure a mail gateway (like Exchange Online Protection) to handle plus addressing
• Use mail-enabled contacts with specific address policies
• Implement a custom SMTP receive connector with address rewriting

After implementation, verify with these PowerShell commands:

Test-Mailflow -TargetEmailAddress "test+validation@domain.com"
Get-MessageTrackingLog -Recipients "test@domain.com" -StartDate (Get-Date).AddHours(-1)

Check message headers for proper handling of the plus address in the X-Original-To header.

Microsoft Exchange Server doesn't natively support plus addressing (+tag) functionality like Sendmail does. The "+" character isn't treated as a special delimiter in Exchange's email routing engine. However, there are several alternative approaches to achieve similar functionality:

You can create transport rules to handle plus addresses, though this requires explicit configuration for each variation:

New-TransportRule -Name "PlusAddressing" 
    -RecipientAddressMatchesPatterns '^(.+)\+.*@domain\.com$'
    -CopyToMessageHeader "X-Original-To"
    -SetHeaderName "To" 
    -SetHeaderValue '$1@domain.com'

A more flexible approach involves using mail flow rules with regex pattern matching:

# PowerShell script for Exchange Management Shell
$rule = New-TransportRule -Name "PlusAddressHandler" 
    -Priority 0 
    -Enabled $true 
    -RecipientAddressMatchesPatterns '^(?[^+]+)(\+[^@]*)?@domain\.com$'
    -SetHeaderName "X-Original-Recipient" 
    -SetHeaderValue '$0' 
    -SetHeaderName "To" 
    -SetHeaderValue '${user}@domain.com'

For more sophisticated implementations, consider:

• Custom SMTP Receive Connector with address rewriting
• Third-party add-ons like CodeTwo Email Address Manager
• Pre-processing via Edge Transport server

Here's a complete PowerShell script that implements plus addressing with logging:

# Exchange Plus Addressing Implementation
$logPath = "C:\ExchangeLogs\PlusAddressing.log"
$domain = "yourdomain.com"

function Log-Message {
    param([string]$message)
    "$(Get-Date -Format 'yyyy-MM-dd HH:mm:ss') - $message" | Out-File $logPath -Append
}

try {
    $rule = Get-TransportRule "PlusAddressHandler" -ErrorAction SilentlyContinue
    if (-not $rule) {
        New-TransportRule -Name "PlusAddressHandler" 
            -RecipientAddressMatchesPatterns "^(.+)\+.*@$domain$" 
            -SetHeaderName "X-Original-To" 
            -SetHeaderValue '$0' 
            -SetHeaderName "To" 
            -SetHeaderValue '$1@$domain' 
            -Comments "Handles plus addressing similar to Sendmail"
        
        Log-Message "Plus addressing rule created successfully"
    }
    else {
        Set-TransportRule "PlusAddressHandler" 
            -RecipientAddressMatchesPatterns "^(.+)\+.*@$domain$"
        
        Log-Message "Plus addressing rule updated"
    }
}
catch {
    Log-Message "Error configuring plus addressing: $_"
    throw
}