Fix Email Not Sending

What's Actually Happening

Emails are not being delivered. Outbound emails fail, bounce back, or are marked as spam. SMTP connections fail or timeout.

The Error You'll See

SMTP connection failed:

```bash telnet smtp.example.com 587

Connection refused ```

Authentication error:

535 5.7.8 Username and Password not accepted

Bounce message:

554 5.7.1 Message rejected: Email blocked by spam filter

Why This Happens

1. 1.SMTP server down - Email server not running
2. 2.Wrong credentials - Invalid username/password
3. 3.Port blocked - Firewall blocking SMTP ports
4. 4.DNS issues - MX record misconfigured
5. 5.SPF/DKIM failure - Missing authentication records
6. 6.Rate limited - Sending limit exceeded
7. 7.Blacklisted - IP address blacklisted

Step 1: Check SMTP Connectivity

```bash # Test SMTP port: nc -zv smtp.example.com 25 nc -zv smtp.example.com 587 nc -zv smtp.example.com 465

# Test with telnet: telnet smtp.example.com 25

# Test with openssl (TLS): openssl s_client -connect smtp.example.com:587 -starttls smtp openssl s_client -connect smtp.example.com:465

# Ping test: ping -c 3 smtp.example.com ```

Step 2: Check Mail Server Status

```bash # Postfix: systemctl status postfix

postfix check

postconf -n

# Sendmail: systemctl status sendmail

# Exim: systemctl status exim

# Check mail queue: mailq postqueue -p

# Flush queue: postqueue -f ```

Step 3: Check Authentication

```bash # Test authentication: telnet smtp.example.com 587 # EHLO localhost # STARTTLS # AUTH LOGIN

# Check SASL: testsaslauthd -u username -p password

# Postfix SASL: cat /etc/postfix/sasl_passwd

postmap /etc/postfix/sasl_passwd

# Check credentials: echo -n "username" | base64 echo -n "password" | base64 ```

Step 4: Check DNS and MX Records

```bash # Check MX records: dig MX example.com

nslookup -type=MX example.com

# Check A record: dig A mail.example.com

# Check reverse DNS: dig -x 1.2.3.4

# SPF record: dig TXT example.com | grep v=spf1

# DKIM: dig TXT selector._domainkey.example.com

# DMARC: dig TXT _dmarc.example.com ```

Step 5: Check Firewall

```bash # Check outbound ports: iptables -L OUTPUT -n | grep -E "25|587|465"

# Allow SMTP: iptables -I OUTPUT -p tcp --dport 25 -j ACCEPT iptables -I OUTPUT -p tcp --dport 587 -j ACCEPT iptables -I OUTPUT -p tcp --dport 465 -j ACCEPT

# UFW: ufw allow out 25/tcp ufw allow out 587/tcp ufw allow out 465/tcp

# Firewalld: firewall-cmd --add-port=587/tcp firewall-cmd --reload ```

Step 6: Check Mail Logs

```bash # Postfix logs: tail -f /var/log/mail.log

journalctl -u postfix -f

# Look for: grep -i "error|fail|reject" /var/log/mail.log | tail -20

# Sendmail logs: tail -f /var/log/maillog

# Check delivery: grep "status=sent" /var/log/mail.log | tail -10 grep "status=bounced" /var/log/mail.log | tail -10 ```

Step 7: Check for Blacklisting

```bash # Check IP reputation: # - https://mxtoolbox.com/blacklists.aspx # - https://www.spamhaus.org/ # - https://www.spamcop.net/

# Check with dig: dig 4.3.2.1.zen.spamhaus.org

# If listed: # 1. Fix the issue (stop spam, secure server) # 2. Request delisting ```

Step 8: Test Email Sending

```bash # Send test email: echo "Test message" | mail -s "Test Subject" user@example.com

# Send with swaks: swaks --to user@example.com --from sender@example.com --server smtp.example.com

# Send with telnet: telnet smtp.example.com 25 HELO localhost MAIL FROM: sender@example.com RCPT TO: user@example.com DATA Subject: Test Test message . QUIT

# Send with curl: curl --url 'smtp://smtp.example.com:587' \ --mail-from 'sender@example.com' \ --mail-rcpt 'user@example.com' \ --upload-file email.txt \ --user 'username:password' ```

Step 9: Check Rate Limits

```bash # Postfix rate limiting: postconf | grep smtp_destination_rate_delay

# Gmail limits: # 500 emails/day for free accounts # 2000 emails/day for G Suite

# AWS SES limits: aws ses get-send-quota

# Check provider documentation for limits ```

Step 10: Monitor Email Delivery

```bash # Monitor mail queue: watch -n 5 'mailq | head -20'

# Check delivery status: tail -f /var/log/mail.log | grep "status="

# Postfix statistics: postfix-stats

# Use monitoring tools: # - Mailchimp reports # - SendGrid dashboard # - AWS SES console ```

Email Not Sending Checklist

Verify the Fix

```bash nc -zv smtp.example.com 587

systemctl status postfix

echo "Test" | mail -s "Test" user@example.com

tail -f /var/log/mail.log

dig MX example.com

grep "status=sent" /var/log/mail.log | tail -5 ```

Related Issues

• [Fix Email Going to Spam](/articles/fix-email-going-to-spam)
• [Fix Email Authentication Failed](/articles/fix-email-authentication-failed)
• [Fix DNS Resolution Failed](/articles/fix-dns-resolution-failed)