To send an email with a file attachment using /usr/sbin/sendmail -t, you need to construct a MIME-formatted email. The MIME format allows you to include attachments along with text content.

Script to Send an Email with an Attachment

#!/bin/bash

# Variables
TO="recipient@example.com"
SUBJECT="Email with Attachment"
BODY="Hello,\n\nPlease find the attached file.\n\nBest regards,\nYour Script"
ATTACHMENT="example.txt" # Path to the file you want to attach

# Create a unique boundary string
BOUNDARY="====MULTIPART_BOUNDARY_$(date +%s)===="

# Create the email headers
{
    echo "To: $TO"
    echo "Subject: $SUBJECT"
    echo "MIME-Version: 1.0"
    echo "Content-Type: multipart/mixed; boundary=\"$BOUNDARY\""
    echo
    echo "This is a multi-part message in MIME format."
    echo
    # Add the email body
    echo "--$BOUNDARY"
    echo "Content-Type: text/plain; charset=\"utf-8\""
    echo "Content-Transfer-Encoding: 7bit"
    echo
    echo -e "$BODY"
    echo
    # Add the attachment
    echo "--$BOUNDARY"
    echo "Content-Type: $(file --mime-type -b "$ATTACHMENT")"
    echo "Content-Transfer-Encoding: base64"
    echo "Content-Disposition: attachment; filename=\"$(basename "$ATTACHMENT")\""
    echo
    base64 "$ATTACHMENT"
    echo
    # End the email
    echo "--$BOUNDARY--"
} | /usr/sbin/sendmail -t

Explanation

  1. Headers:
    • The script sets MIME-Version, Content-Type, and boundary to format the email as MIME.
    • boundary separates different parts of the email (body and attachments).
  2. Body:
    • The plain text content is added under Content-Type: text/plain.
  3. Attachment:
    • The file is encoded in base64 to ensure it is sent properly over email.
    • The Content-Disposition header includes the filename.
  4. Sendmail:
    • The formatted email is piped to /usr/sbin/sendmail -t for delivery.

How to Use the Script

1 Create the File to Attach:

Create a text file (e.g., example.txt) to attach.

echo "This is the content of the file." > example.txt
2 Save the Script:

Save the script to a file, e.g., send_email_with_attachment.sh.

3 Make the Script Executable:
chmod +x send_email_with_attachment.sh
4 Run the Script:
./send_email_with_attachment.sh

Requirements

  1. Sendmail Installed:

    Ensure sendmail is installed and configured on your system.

    sudo apt install sendmail # Debian/Ubuntu
    sudo yum install sendmail # CentOS/RHEL
  2. Valid Mail Configuration:

    Check that your server can send emails using sendmail. Test with a simple email:

    echo "Test email" | /usr/sbin/sendmail -t recipient@example.com

Troubleshooting

  1. Attachment Corruption:
    • Ensure the file is properly encoded using base64.
  2. Email Not Delivered:
    • Check the mail logs for issues:
      • tail -f /var/log/mail.log
  3. Permission Issues:
    • Ensure the script and attachment file have the correct read permissions.
  4. Email Marked as Spam:
    • Configure SPF, DKIM, and DMARC for your email domain.

This script demonstrates how to send an email with a file attachment using /usr/sbin/sendmail -t by properly formatting the email with MIME types and base64 encoding.