Troubleshooting Common MailChannels Setup Errors

Getting started with MailChannels is typically smooth, but like any email infrastructure, issues can pop up during setup. Whether you’re integrating via SMTP or API, a misstep in configuration can delay your ability to send critical transactional emails like password resets, alerts, or order confirmations.

This guide walks through the most common MailChannels setup errors and how to fix them fast, so you can start sending with confidence.

1. SMTP Authentication Fails

Symptoms:

• Connection errors when sending via smtp.mailchannels.net
  
• “Authentication failed” or “535 5.7.8” errors in logs
  

Causes:

• Incorrect username or password
  
• Missing STARTTLS or SSL configuration
  
• Using port 25 (commonly blocked)
  

Fix:

• Double-check your credentials in your MailChannels dashboard
  
• Use port 587 (with STARTTLS) or 465 (with SSL)
  
• Ensure authentication is enabled in your mail client
  

Learn how to set it up: How to Send Transactional Email via SMTP Relay

2. Emails Not Arriving (but no errors in logs)

Symptoms:

• No bounce, no delivery
  
• Email appears “sent” from your app but never reaches inbox
  

Causes:

• SPF or DKIM misconfiguration
  
• Recipient server silently drops the message
  
• Spam filter catching the email
  

Fix:

• Ensure your DNS includes:
  
  • ✅ SPF record with MailChannels sending domain
    
  • ✅ DKIM keys published correctly
    
  • ✅ A clear From: domain that matches your authenticated domain
    
• Check spam folders and delivery headers
  
• Use inbox testing tools to trace where messages stop
  

Related: Key Components of a Transactional Email

3. API Requests Returning 400 or 401 Errors

Symptoms:

• API returns 400 (Bad Request) or 401 (Unauthorized)
  

Causes:

• Invalid or missing API key
  
• Incorrect Content-Type or payload format
  
• Authorization header not set properly
  

Fix:

• Use the correct Bearer token in the header:
  

Authorization: Bearer YOUR_API_KEY

• 
  Ensure Content-Type: application/json is set
  
• Validate your JSON payload with a linter or schema
  

Check this guide: How to Integrate the MailChannels Email API (with Code Examples)

4. High Bounce or Rejection Rates

Symptoms:

• Many emails show up as bounced or rejected
  
• Low inbox placement or throttling
  

Causes:

• Sending to unverified or stale email lists
  
• Sudden spike in volume without IP/domain warm-up
  
• Lack of proper domain authentication
  

Fix:

• Clean your email lists and only send to verified addresses
  
• Implement an IP warmup strategy
  
• Use double opt-in for new signups to avoid typo traps
  

5. Port 25 Blocked by Hosting Provider

Symptoms:

• Your app or server cannot connect to MailChannels SMTP endpoint
  
• “Connection timed out” or network-level errors
  

Causes:

• Many cloud providers (e.g., AWS, GCP, DigitalOcean) block outbound port 25 by default
  

Fix:

• Use port 587 with STARTTLS instead
  
• If your host blocks all SMTP, switch to the MailChannels Email API
  

6. TLS/SSL Errors

Symptoms:

• “Cannot establish TLS connection” or handshake failures
  
• Errors when trying to send encrypted messages
  

Causes:

• Outdated libraries or ciphers
  
• Improper STARTTLS command ordering
  

Fix:

• Ensure your client is up to date and supports TLS 1.2+
  
• For SMTP, initiate STARTTLS before sending credentials
  
• For API, verify HTTPS is properly enabled and no proxies are intercepting traffic
  

7. Message Blocked Due to Spam-Like Content

Symptoms:

• Message rejected by MailChannels with error related to content
  
• Logs show spam filtering events
  

Causes:

• Message body or headers triggering spam rules
  
• No unsubscribe links (for non-transactional content)
  
• Overuse of marketing language in subject lines
  

Fix:

• Ensure the email is purely transactional
  
• Avoid excessive use of ALL CAPS, exclamation marks, or misleading subjects
  
• Use neutral, action-based language like “Verify your account” or “Your receipt is ready”
  

Want clarity on what counts as transactional? What Is Transactional Email? (vs Marketing Email)

Final Thoughts

Small misconfigurations can prevent your emails from reaching the inbox, but once you’ve addressed SPF, DKIM, port settings, and formatting errors, MailChannels provides a reliable and secure path for your transactional email.

Still stuck? Our support team is built around email delivery expertise, not just ticket triage. Reach out through your dashboard, or visit MailChannels Email API to start fresh.