Setting appropriate email attachment limits is more nuanced than simply picking an arbitrary number. While many admins default to 10-20MB with the standard "email isn't for file transfers" disclaimer, modern Exchange environments demand a more systematic approach.

When determining attachment size limits for an Exchange 2007 environment with 50 mailboxes (mixed 2007/2003 clients), consider these technical aspects:

• Storage Infrastructure: Calculate available storage against expected email volume
• Network Bandwidth: Evaluate internal and external bandwidth constraints
• Recipient Limitations: Consider compatibility with external recipients' systems
• Transport Pipeline: Assess message processing capabilities

Here's a PowerShell script to analyze mailbox usage patterns and suggest limits:

# Exchange 2007 Attachment Size Analyzer
$mailboxes = Get-Mailbox -ResultSize Unlimited
$attachmentStats = @()

foreach ($mbx in $mailboxes) {
    $stats = Get-MailboxStatistics -Identity $mbx.Identity | Select DisplayName,TotalItemSize
    $largeItems = Get-MessageTrackingLog -ResultSize Unlimited -Start (Get-Date).AddDays(-30) 
                -EventId "RECEIVE" -Server $env:COMPUTERNAME | 
                Where { $_.Sender -eq $mbx.PrimarySmtpAddress -and $_.TotalBytes -gt 10MB }
    
    $attachmentStats += [PSCustomObject]@{
        Mailbox = $mbx.DisplayName
        AvgAttachmentSize = ($largeItems | Measure-Object -Property TotalBytes -Average).Average
        MaxAttachmentSize = ($largeItems | Measure-Object -Property TotalBytes -Maximum).Maximum
        LargeItemCount = $largeItems.Count
    }
}

$attachmentStats | Export-Csv -Path "C:\Reports\AttachmentAnalysis.csv" -NoTypeInformation

When configuring limits in Exchange 2007:

# Set organization-wide limits
Set-TransportConfig -MaxSendSize 25MB -MaxReceiveSize 25MB

# Optional per-mailbox overrides
Get-Mailbox | Set-Mailbox -MaxSendSize 25MB -MaxReceiveSize 25MB

# Configure connectors if needed
Get-ReceiveConnector | Set-ReceiveConnector -MaxMessageSize 25MB
Get-SendConnector | Set-SendConnector -MaxMessageSize 25MB

For environments frequently needing larger file transfers:

• Implement secure FTP with automated email notifications
• Configure SharePoint document libraries with email alerts
• Deploy a dedicated file sharing solution with Outlook integration

Create a scheduled task to monitor NDRs caused by size limits:

# NDR Monitoring Script
$ndrReports = Get-MessageTrackingLog -ResultSize Unlimited -Start (Get-Date).AddDays(-7) 
             -EventId "FAIL" | Where { $_.MessageSubject -match "exceeded maximum" }

if ($ndrReports.Count -gt 0) {
    Send-MailMessage -To "admin@domain.com" -Subject "NDR Alert" 
    -Body "There were $($ndrReports.Count) NDRs related to size limits this week" 
    -SmtpServer "mail.domain.com"
}

Setting attachment size limits often feels like throwing darts blindfolded. Many admins default to arbitrary values like 10-20MB with the standard "email isn't for file transfers" justification. But when implementing a new Exchange Server (especially in mixed 2007/2013 environments), we need a more systematic approach.

For an environment with 50 mailboxes, consider these technical parameters:

// Pseudocode for calculating attachment limits
function calculateAttachmentLimit() {
  const storageCapacity = getExchangeStorage(); // in GB
  const dailyMessages = getAverageMessageCount();
  const avgMessageSize = getMessageSizeMetrics();
  const bandwidth = getNetworkBandwidth();
  
  // Calculate base limit considering 20% of average daily traffic
  const baseLimit = (storageCapacity * 1024) / (dailyMessages * 0.2);
  
  // Adjust for network constraints
  const networkAdjustedLimit = Math.min(baseLimit, bandwidth / 2);
  
  return formatSize(networkAdjustedLimit);
}

For Exchange 2007/2013 hybrid environments, use PowerShell to set consistent limits:

# Set global transport limits
Set-TransportConfig -MaxSendSize 25MB -MaxReceiveSize 25MB

# Set mailbox server limits
Get-MailboxServer | Set-MailboxServer -MaxSendSize 25MB -MaxReceiveSize 25MB

# Set individual mailbox limits (if needed)
Get-Mailbox -ResultSize Unlimited | Set-Mailbox -MaxSendSize 25MB -MaxReceiveSize 25MB

Implement monitoring to validate your limits:

# PowerShell script to monitor attachment sizes
$report = Get-MessageTrackingLog -Start (Get-Date).AddDays(-30) -EventId RECEIVE | 
          Where-Object {$_.TotalBytes -gt 10MB} | 
          Select-Object Timestamp,Sender,Recipients,MessageSubject,TotalBytes |
          Sort-Object TotalBytes -Descending

$report | Export-Csv -Path "LargeAttachmentsReport.csv" -NoTypeInformation

• Align limits with your backup window and storage retention policies
• Consider implementing message size limits per recipient count
• For frequent large file transfers, integrate with SharePoint or OneDrive

For more advanced environments, consider dynamic limits based on:

// C# example for dynamic limit calculation
public class AttachmentLimitCalculator {
    public double CalculateDynamicLimit(DateTime time, string sender) {
        var baseLimit = 25.0; // MB
        var adjustment = 0.0;
        
        // Reduce limits during business hours
        if (time.Hour >= 8 && time.Hour <= 18) {
            adjustment -= 5.0;
        }
        
        // Increase limits for executives
        if (IsExecutiveSender(sender)) {
            adjustment += 10.0;
        }
        
        return Math.Max(10.0, baseLimit + adjustment);
    }
}