Email errors & SMTP issues

Email errors & SMTP issues #

Email errors & SMTP issues help you diagnose and resolve problems related to email sending, delivery, and configuration.

This guide covers common SMTP errors, delivery failures, and how to fix them step by step.

When to use email errors & SMTP issues #

Use email errors & SMTP issues when:

• Emails are not delivered
• SMTP validation fails
• Campaigns are not sending
• Emails go to spam or are rejected

Email errors & SMTP issues checklist #

Before troubleshooting specific problems, check:

1. SMTP server is configured correctly
2. Mailbox is connected
3. Email template is valid
4. Campaign is active

👉 Setup guide:
Email setup: SMTP & mailbox guide

SMTP authentication failed (535) in email errors & SMTP issues #

Error:
SMTP 535 Authentication Failed

Possible causes:

• Incorrect username or password
• Authentication disabled
• Invalid SMTP credentials

How to fix:

1. Verify SMTP username and password
2. Enable authentication in your email provider
3. Re-enter credentials and save

Email rejected (550) in email errors & SMTP issues #

Error:
SMTP 550 Message Rejected

Possible causes:

• Recipient server blocked the message
• Sender reputation issues
• Invalid recipient address

How to fix:

1. Verify recipient email address
2. Check sender reputation
3. Avoid spam-like content

Service not available (421) in email errors & SMTP issues #

Error:
SMTP 421 Service Not Available

Possible causes:

• Temporary server issue
• Rate limiting
• Provider restrictions

How to fix:

1. Wait and retry
2. Reduce sending rate
3. Check provider status

Emails not delivered in email errors & SMTP issues #

Possible causes:

• SMTP not configured
• Invalid email addresses
• Spam filtering

How to fix:

1. Verify SMTP setup
2. Clean contact list
3. Send test email

👉 See:
Email templates: create & use easily

Emails going to spam in email errors & SMTP issues #

Possible causes:

• Missing SPF/DKIM/DMARC
• Poor content quality
• Low sender reputation

How to fix:

1. Configure SPF, DKIM, DMARC
2. Improve email content
3. Avoid spam triggers

Campaign not sending in email errors & SMTP issues #

Possible causes:

• SMTP server not selected
• Mailbox not configured
• Template missing

How to fix:

1. Select correct SMTP server
2. Assign reply-to mailbox
3. Choose valid template

👉 See:
Email campaigns: create & send

Mailbox not receiving replies #

Possible causes:

• IMAP/POP3 misconfiguration
• Mailbox not connected
• Access denied

How to fix:

1. Verify mailbox settings
2. Reconnect mailbox
3. Test connection

Common email errors & SMTP issues scenarios #

Emails sent but not opened #

Reason:

• Subject not engaging
• Emails filtered

Solution:

• Improve subject line
• Test different content

Emails delayed #

Reason:

• Provider queue
• Rate limiting

Solution:

• Monitor sending rate
• Retry later

Best practices for email errors & SMTP issues #

• Use a reliable SMTP provider
• Always test before sending campaigns
• Configure SPF, DKIM, DMARC
• Keep contact lists clean
• Monitor delivery performance

Related guides #

• 👉 Email setup: SMTP & mailbox guide
• 👉 Email templates: create & use easily
• 👉 Email campaigns: create & send
• 👉 General troubleshooting guide