Why Does Email Block Attachments?

Email services block potentially dangerous file types to protect users from malware, viruses, and phishing attacks. Executable files (.exe, .bat, .com), scripts (.js, .vbs, .ps1), and archives containing them are commonly blocked by Gmail, Outlook, Yahoo Mail, and corporate email systems. Understanding these security measures helps you find safe alternatives for sending legitimate files.

Why Email Services Block Attachments

1. Malware and Virus Protection

Email is the #1 delivery method for malware. Cybercriminals disguise viruses, ransomware, and trojans as seemingly innocent attachments like invoices, receipts, or documents.

Common attack vectors:

• Executable files: .exe, .msi, .com, .bat files directly run code
• Office macros: Word/Excel files with malicious VBA scripts
• Script files: .js, .vbs, .ps1 can execute harmful commands
• Disguised extensions: invoice.pdf.exe (looks like PDF, actually executable)
• Compressed malware: .zip/.rar files containing dangerous files

2. Phishing and Social Engineering

Attackers send malicious files designed to steal credentials, financial data, or install spyware. Email providers block high-risk file types to prevent users from inadvertently running these files.

3. Corporate Security Policies

Organizations implement strict email filtering to protect intellectual property, comply with regulations (HIPAA, GDPR, PCI DSS), and prevent data breaches. IT departments block file types based on risk assessment.

4. File Size Limitations

Email was designed for text messages, not large file transfers. Most providers limit attachment size:

• Gmail: 25 MB (total message size)
• Outlook.com: 20 MB
• Yahoo Mail: 25 MB
• Corporate Exchange: Varies, often 10-25 MB

Commonly Blocked File Types

Executables and Programs

• .exe - Windows executable
• .com - DOS executable
• .bat - Batch script
• .cmd - Command script
• .msi - Windows installer
• .scr - Screen saver (can be malicious)
• .pif - Program information file
• .app - macOS application

Script Files

• .js - JavaScript
• .jse - Encoded JavaScript
• .vbs - Visual Basic Script
• .vbe - Encoded VBS
• .ps1 - PowerShell script
• .wsf - Windows Script File
• .jar - Java archive (executable)

Office Files with Macros

• .docm - Word document with macros
• .xlsm - Excel spreadsheet with macros
• .pptm - PowerPoint with macros
• .dotm - Word template with macros

Archives Containing Blocked Types

• .zip with .exe inside
• .rar with scripts
• .7z containing executables
• Password-protected archives (can't scan contents)

Specialized File Types

• .reg - Registry files (modify Windows registry)
• .dll - Dynamic link libraries
• .ocx - ActiveX controls
• .sys - System files
• .inf - Setup information files

Email Provider Blocking Policies

Gmail

Blocks: Executables, scripts, archives containing blocked types

Error message: "Blocked for security reasons"

Special notes:

• Scans all attachments with antivirus
• Automatically converts large files to Google Drive links
• Blocks even if extension is changed (inspects file headers)

Outlook.com / Microsoft 365

Blocks: Comprehensive list of dangerous extensions

Error message: "This file type isn't allowed"

Special notes:

• Offers OneDrive integration for large files
• Administrators can customize blocked list for organizations
• Some files allowed with warnings rather than hard blocks

Yahoo Mail

Blocks: Executables, scripts, suspicious archives

Similar policies to Gmail and Outlook

Corporate Email (Exchange, G Suite)

Highly customizable: IT departments define policies

May include:

• DLP (Data Loss Prevention) scanning
• Encrypted file requirements
• Quarantine for manual review
• Whitelist-only external attachments

Safe Methods to Send Blocked Files

Method 1: Cloud Storage Links (Best Practice)

Advantages:

• Bypasses email filters completely
• No file size limits (or much higher limits)
• Recipients can download at their convenience
• Links can be password protected
• Professional appearance

Method 2: Compress with Password Protection

Method 3: Rename File Extension (Temporary)

Method 4: Convert to Different Format

Sometimes you can convert files to allowed formats:

• Scripts: Paste code into .txt file with instructions
• Documents: Convert .docm to .docx (removes macros)
• Data files: Convert to CSV or JSON text formats
• Images: Convert to PDF

Use our file converter tools for format conversion.

Method 5: Specialized File Transfer Services

For large or sensitive files:

• Send Anywhere: Direct P2P transfer, no cloud storage
• Firefox Send alternative (Send-Encrypted): Encrypted, self-destructing links
• OnionShare: Anonymous file sharing via Tor
• Tresorit Send: End-to-end encrypted transfers

Receiving Blocked Attachments

If someone tries to send you blocked files:

Corporate Email Specific Solutions

For IT Administrators

Balance security with productivity:

• Whitelist trusted domains: Allow certain file types from verified partners
• Sandboxing: Execute attachments in isolated environments before delivery
• User training: Educate employees about phishing and safe file handling
• DLP policies: Scan content, not just file types
• Secure file portals: Provide approved file transfer solutions

For Employees

• Use company-approved file sharing solutions
• Contact IT before attempting workarounds
• Never bypass security for convenience
• Request whitelisting for legitimate business partners

Security Best Practices

Before Opening Any Attachment

• Verify sender: Confirm email address is legitimate (not spoofed)
• Check for urgency tactics: "Act now!" and threats are red flags
• Scan with antivirus: Even if file type seems safe
• Check file properties: View real extension, file size
• Hover over links: Don't click if URL looks suspicious

Red Flags for Malicious Attachments

• Unexpected attachments from known contacts (compromised account)
• Generic greetings ("Dear Customer" instead of your name)
• Grammar and spelling errors
• Mismatch between email content and attachment
• Double extensions (invoice.pdf.exe)
• Unusual sender addresses (paypa1.com vs paypal.com)

Safe File Types

Generally safe to receive (but still scan):

• Images: .jpg, .png, .gif (large files could still contain malware)
• Documents: .pdf, .docx, .xlsx (without macros)
• Text: .txt, .csv, .log
• Audio/Video: .mp3, .mp4 (from trusted sources)

Troubleshooting Legitimate Blocks

If you legitimately need to send software or scripts:

Future of Email Attachment Security

Email security continues evolving:

• AI-powered filtering: Machine learning detects zero-day threats
• Sandboxing everywhere: Execute attachments in isolated environments
• Blockchain verification: Cryptographic sender verification
• Reduced attachment use: Trend toward link-based sharing