Heredoc vs echo — when which?

Heredoc for multi-line messages with embedded headers: `sendmail -t

Cron job uses same script — works on CLI but cron mail bounces?

Cron's environment differs from interactive shell. PATH limited, no TTY, no working dir. sendmail might not be in cron's PATH. Use full path `/usr/sbin/sendmail` in cron scripts. Or set PATH in crontab (`PATH=/usr/sbin:/usr/bin:/bin`).

How do I include attachments?

Manual MIME assembly with sendmail -t is painful. Use mutt: `mutt -a /path/file.pdf -s 'Subject' -- user@example.com < body.txt`. Handles MIME, encoding, boundary. Or PHP's PHPMailer for app-driven mail. Raw sendmail -t is for plain-text only.

header injection vulnerability — what to watch?

If you pipe user input into sendmail, attackers can inject CRLF + new headers (Bcc, fake From). Validate/sanitize input strictly. PHP's mail() with sendmail -t backend is vulnerable to header injection if you put user data in headers. Use a proper mail library which handles this.

Using /usr/sbin/sendmail -t to Send an Email from the Command Line

Q: header injection vulnerability — what to watch?

If you pipe user input into sendmail, attackers can inject CRLF + new headers (Bcc, fake From). Validate/sanitize input strictly. PHP's mail() with sendmail -t backend is vulnerable to header injection if you put user data in headers. Use a proper mail library which handles this.

2 min read

12.10.2025

The /usr/sbin/sendmail -t command allows you to send emails directly from the command line on Unix-like systems. It reads the recipients from the email headers (e.g., To, Cc, Bcc) within the email content. This method is commonly used for automation in scripts or cron jobs.

sendmail -t Command Line — sendmail -t CLI — quick scripts; mutt for more polished use.

For closely related sendmail / script-mail topics, see Using /usr/sbin/sendmail -bs, /usr/sbin/sendmail -t -i, What is /usr/sbin/sendmail -t -i?, and sendmail -fcrondaemon — cron variant.

Steps to Send an Email with /usr/sbin/sendmail -t

Create the Email Content

The email content must include the headers (e.g., To, Subject) followed by the message body.

Example file (email.txt):

To: recipient@example.com Subject: Test Email from Command Line Hello, This is a test email sent using /usr/sbin/sendmail -t. Best regards, Your Server

Use the sendmail Command

Run the following command to send the email:

/usr/sbin/sendmail -t < email.txt

-t: Instructs sendmail to read the recipient addresses (To, Cc, Bcc) from the email headers.
< email.txt: Feeds the email content to the command.

Example: Combining with echo and heredoc

Using echo:

echo -e "To: recipient@example.com\nSubject: Test Email\n\nThis is the body of the email." | /usr/sbin/sendmail -t

Using a Heredoc:

/usr/sbin/sendmail -t <



    Use Cases
    
        
            Automation
            Ideal for sending system alerts or logs in scripts.
            Example:
            
                echo -e "To: admin@example.com\nSubject: Backup Completed\n\nThe backup was successful." | /usr/sbin/sendmail -t
            
        
        
            Cron Jobs
            Send output or error notifications from scheduled tasks.
            Example cron entry:
            
                0 2 * * * /path/to/script.sh | /usr/sbin/sendmail -t
            
        
        
            Testing Email Server Configuration
            Useful for verifying if sendmail is properly configured.
        
    

    Troubleshooting Common Issues
    

        
            
                Issue
                Solution
            
        
        
            
                Command Not Found
                
                    
                        Verify if sendmail is installed: which sendmail
                        If not installed, install a compatible Mail Transfer Agent (MTA), such as Postfix:
                            
                                sudo apt install postfix
                            
                        
                    
                
            
            
                Emails Not Delivered
                
                    
                        Check the mail queue for stuck messages: mailq
                        Examine the mail logs:
                            
                                Postfix: sudo tail -f /var/log/mail.log
                                Exim: sudo tail -f /var/log/exim_mainlog
                            
                        
                    
                
            
            
                Emails Marked as Spam
                
                    Ensure the sender domain has correct DNS records:
                    
                        SPF: Authorizes the server to send emails.
                        DKIM: Digitally signs emails.
                        DMARC: Defines email handling policies.
                    
                
            
            
                Debugging the Sendmail Command
                
                    Use verbose mode to see detailed output:
                    
                        echo -e "To: recipient@example.com\nSubject: Test Email\n\nBody content" | /usr/sbin/sendmail -t -v
                    
                
            
        
    

    Enhancements and Alternatives
    
        
            Use a Lightweight Mail Client:
                Instead of sendmail, consider using mailx or msmtp for simpler email sending:
                
                    echo "This is a test email" | mail -s "Subject" recipient@example.com
                
            
            Send Emails via SMTP:
                Use tools like Python?s smtplib or a service like SendGrid for more control and security.

Issue	Solution
Command Not Found	Verify if sendmail is installed: which sendmail If not installed, install a compatible Mail Transfer Agent (MTA), such as Postfix: sudo apt install postfix
Emails Not Delivered	Check the mail queue for stuck messages: mailq Examine the mail logs: Postfix: sudo tail -f /var/log/mail.log Exim: sudo tail -f /var/log/exim_mainlog
Emails Marked as Spam	Ensure the sender domain has correct DNS records: SPF: Authorizes the server to send emails. DKIM: Digitally signs emails. DMARC: Defines email handling policies.
Debugging the Sendmail Command	Use verbose mode to see detailed output: echo -e "To: recipient@example.com\nSubject: Test Email\n\nBody content" \| /usr/sbin/sendmail -t -v

Using /usr/sbin/sendmail -t to Send an Email from the Command Line

Steps to Send an Email with /usr/sbin/sendmail -t

Create the Email Content

Use the sendmail Command

Example: Combining with echo and heredoc

Using echo:

Using a Heredoc:

Use Cases

Automation

Cron Jobs

Testing Email Server Configuration

Troubleshooting Common Issues

Enhancements and Alternatives

Hosting

Cloud Solutions

For You

VDS

Website Builders

Our services

Client Area

Using /usr/sbin/sendmail -t to Send an Email from the Command Line

Steps to Send an Email with /usr/sbin/sendmail -t

Create the Email Content

Use the sendmail Command

Example: Combining with echo and heredoc

Using echo:

Using a Heredoc:

Use Cases

Automation

Cron Jobs

Testing Email Server Configuration

Troubleshooting Common Issues

Enhancements and Alternatives

Hosting

Cloud Solutions

For You

VDS

Website Builders

Our services

Client Area

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