Why Do Email Attachments Get Blocked?

Why Do Email Attachments Get Blocked?

Email attachments get blocked for security reasons, file type restrictions, size limits, spam filtering, and policy compliance. Understanding why attachments are blocked helps avoid delivery issues and ensures reliable email communication.

Common reasons include potentially malicious file types, large file sizes, virus threats, corporate security policies, and email client restrictions. Use cloud storage links instead of attachments when possible to avoid blocking issues.

Extract and analyze attachments from emails using our extract email attachments tool to understand attachment structure and identify potential blocking issues.

Security Reasons

1. Malicious File Types

Executable files (.exe, .bat, .scr, .com) and scripts are commonly blocked as they can contain malware or viruses.

2. Virus Scanning

Email servers scan attachments for viruses. Infected files are automatically blocked to protect recipients.

3. Suspicious Patterns

Attachments with suspicious names, double extensions, or unusual characteristics may be blocked as potential threats.

4. Corporate Policies

Organizations implement security policies that block certain file types to prevent security threats and data breaches.

5. Email Client Restrictions

Some email clients block attachments by default or restrict certain file types for security reasons.

File Type Restrictions

Certain file types are commonly blocked due to security concerns:

Executable Files

• .exe (Windows executables)
• .bat, .cmd (Batch scripts)
• .scr (Screen savers - can contain malware)
• .com (Command files)
• .pif (Program Information Files)

Script Files

• .js (JavaScript)
• .vbs (VBScript)
• .ps1 (PowerShell scripts)
• .sh (Shell scripts)

Archive Files

.zip, .rar, and other archives may be blocked if they contain executables or are password-protected (preventing virus scanning).

Size Limits

Email Server Limits

Email servers impose size limits on attachments (typically 10-25MB). Attachments exceeding limits are rejected or blocked.

Email Client Limits

Email clients may have their own size restrictions, blocking large attachments even if server allows them.

Network Limitations

Large attachments can cause delivery delays, timeouts, or blocking due to network constraints.

Best Practice

Keep attachments under 10MB when possible. Use cloud storage links for larger files instead of email attachments.

How to Avoid Blocking

1. Use Safe File Types

Use commonly accepted file types like .pdf, .docx, .xlsx, .jpg, .png that are less likely to be blocked.

2. Keep Files Small

Keep attachment sizes under 10MB to avoid size limit blocking. Compress files when possible.

3. Use Cloud Storage

Share files via cloud storage links (Google Drive, Dropbox, OneDrive) instead of email attachments for better reliability.

4. Scan for Viruses

Scan attachments for viruses before sending to avoid virus scanner blocking.

5. Avoid Executables

Never send executable files or scripts as attachments. Use cloud storage links instead.

6. Test Attachments

Test attachment delivery before sending important emails to ensure they're not blocked.