SMTP errors occur when an email cannot be sent from your email account.
This means the message is blocked or rejected before delivery.

SMTP errors are usually configuration-related.

What SMTP Is #

SMTP stands for Simple Mail Transfer Protocol.
It is the system used to send outgoing email from your mailbox to other servers.

If SMTP fails, outgoing email will not be delivered.

Common SMTP Error Symptoms #

You may experience:

• Error messages when sending email
• Emails stuck in the outbox
• Immediate send failures
• Bounce-back messages with error codes

These indicate a sending issue.

Most Common Causes #

Incorrect SMTP Settings #

Wrong server details will block sending.

Verify:

• SMTP server hostname
• Port number
• Encryption method
• Authentication is enabled

Use the settings shown in cPanel under Connect Devices.

Incorrect Login Credentials #

SMTP requires authentication.

Check:

• Full email address as username
• Correct password
• No extra spaces

Incorrect credentials cause authentication failures.

Wrong Port or Encryption #

Using the wrong combination of:

• Port
• SSL or TLS
• Encryption type

will cause SMTP connection failures.

ISP or Network Blocking #

Some networks block SMTP ports.

If sending works on one network but not another:

• The issue may be network-related
• Try a different port or network

This is common on public or corporate networks.

Account or Mailbox Issues #

Sending may fail if:

• The mailbox is suspended
• Storage limits are exceeded
• The account was recently created and not fully propagated

Check mailbox status in cPanel.

Using Secure SMTP at ProRedLine #

ProRedLine requires:

• Authenticated SMTP
• Secure connections

Plain, unauthenticated SMTP is not supported.

Reading SMTP Error Messages #

Error messages may include:

• Authentication failed
• Connection timed out
• Relay access denied

These messages point to configuration or permission problems.

What You Should Do #

When SMTP errors occur:

1. Recheck SMTP settings in your email client
2. Verify login credentials
3. Try webmail to confirm the account works
4. Test on a different network

These steps resolve most issues.

What You Should Not Do #

Do not:

• Disable authentication
• Repeatedly resend failed messages
• Share email passwords
• Change DNS records for SMTP issues

SMTP errors are not DNS-related.

Responsibility Notice #

You are responsible for:

• Correct email client configuration
• Securing login credentials
• Monitoring mailbox status

ProRedLine does not configure email clients remotely.