When dealing with Sendmail mail storage, several potential locations exist depending on your configuration. The default locations are often overridden in custom setups like yours. Here's how to systematically locate your mail storage:

# Common locations to check:
/var/mail/
/var/spool/mail/
/var/spool/mqueue/
/home/username/mail/

First, examine your Sendmail configuration files to determine the actual mail storage path:

# Check sendmail configuration:
grep -r "Mailbox" /etc/mail/
grep -r "MailDir" /etc/mail/
grep -r "QueueDirectory" /etc/mail/sendmail.cf

# Alternative method using sendmail itself:
sendmail -d0.1 | grep -i mail

For messages that haven't been delivered yet (potentially including your test messages), check the mail queue:

mailq  # Shows current mail queue
sendmail -bp  # Alternative queue view
find /var/spool/mqueue -type f  # Inspect queue files directly

When configuration files don't reveal the location, monitor Sendmail's file operations:

# Linux systems:
strace -f -e trace=file -p $(pgrep sendmail)

# BSD systems:
truss -f -p $(pgrep sendmail) | grep -i mail

Once you've located the mail storage, here's a basic Python autoresponder framework:

#!/usr/bin/env python3
import os
import email
from email.policy import default

MAIL_DIR = "/path/to/your/maildir"  # Replace with your found path

def process_mail(filename):
    with open(filename, 'r') as f:
        msg = email.message_from_file(f, policy=default)
    
    # Extract important headers
    from_addr = msg['from']
    subject = msg['subject']
    
    # Create response
    response = f"""From: your@domain.com
To: {from_addr}
Subject: Re: {subject}

Thank you for your email. This is an automated response.
"""
    
    # Send response (using sendmail directly)
    with os.popen('/usr/sbin/sendmail -t', 'w') as p:
        p.write(response)

for mailfile in os.listdir(MAIL_DIR):
    if mailfile.startswith('new/'):
        process_mail(os.path.join(MAIL_DIR, mailfile))
        # Move to processed folder
        os.rename(
            os.path.join(MAIL_DIR, mailfile),
            os.path.join(MAIL_DIR, 'cur', mailfile)
        )

Some configurations use Maildir format (common with Dovecot or other IMAP servers):

# Sample Maildir structure:
# /home/user/Maildir/
#   ├── cur/
#   ├── new/
#   └── tmp/

# Modified processing logic for Maildir:
def process_maildir(maildir_path):
    new_mail = os.path.join(maildir_path, 'new')
    for mailfile in os.listdir(new_mail):
        full_path = os.path.join(new_mail, mailfile)
        process_mail(full_path)
        # Move to cur with status flags
        os.rename(
            full_path,
            os.path.join(maildir_path, 'cur', f"{mailfile}:2,S")
        )

Sendmail's email storage location depends on multiple configuration factors. Unlike simpler MTAs, Sendmail doesn't have a single default location - it uses a combination of configuration files to determine where to store incoming messages.

First examine these critical configuration files:

# Check sendmail's mail queue directory
grep QueueDirectory /etc/mail/sendmail.cf

# Verify the mail delivery location
grep Mailbox /etc/mail/sendmail.cf

# Check for procmail or other MDA usage
grep Mlocal /etc/mail/sendmail.cf

Here are the most likely locations where your emails might be stored:

• /var/spool/mail/username (traditional BSD-style)
• /var/mail/username (common Linux default)
• /home/username/Maildir/ (for Maildir format)
• ~username/mbox (individual user mailboxes)
• Custom locations defined in /etc/aliases or virtual user tables

Try these diagnostic commands:

# Check active delivery agent
sendmail -d0.1 | grep Mlocal

# Verify mail delivery path
sendmail -bv root

# Examine mail queue
mailq

Once you locate the mail storage, here's a basic Python autoresponder skeleton:

#!/usr/bin/python3
import os
import time
from email.parser import Parser

MAILDIR = "/var/mail/root"  # Update with your actual path

def process_mail():
    with open(MAILDIR, 'r') as f:
        data = f.read()
    emails = data.split('From ')[1:]  # Simple split
    
    for raw_email in emails:
        email = Parser().parsestr('From ' + raw_email)
        response = f"""From: auto-responder@yourdomain.com
To: {email['from']}
Subject: Re: {email['subject']}

Thank you for your email. This is an automated response.
"""
        # Send the response - could use sendmail directly
        with os.popen('/usr/sbin/sendmail -t', 'w') as p:
            p.write(response)

while True:
    process_mail()
    time.sleep(60)  # Check every minute

For better efficiency, consider using inotify to watch the mail file:

import pyinotify

class EventHandler(pyinotify.ProcessEvent):
    def process_IN_MODIFY(self, event):
        process_mail()  # Reuse our previous function

wm = pyinotify.WatchManager()
handler = EventHandler()
notifier = pyinotify.Notifier(wm, handler)
wdd = wm.add_watch(MAILDIR, pyinotify.IN_MODIFY)
notifier.loop()

If emails still aren't appearing:

• Verify Sendmail is actually receiving messages (tail -f /var/log/maillog)
• Check for aliases redirecting mail (grep root /etc/aliases)
• Ensure proper file permissions on mail directories
• Consider whether mail is being delivered to a different user account