Email Not Sending? Complete Troubleshooting Guide
Step-by-step guide to fix email delivery problems: emails stuck in outbox, bouncing back, not received, or going to spam.
When your emails won't send, there are usually just a handful of causes — and most of them are easy to fix. This guide walks you through the most common reasons and solutions.
1. Check Your Internet Connection
This sounds obvious, but it's the most common cause. Your email client needs internet access to connect to the SMTP server. Verify you're online, then try sending again.
2. Check Your SMTP Server Settings
Incorrect SMTP settings are the most common technical cause of sending failures. Verify these settings in your email client:
| Setting | What to Check |
|---|---|
| SMTP Server | Is the hostname correct? (e.g. smtp.gmail.com, not imap.gmail.com) |
| Port | Use 587 (STARTTLS) or 465 (SSL). Avoid port 25 — most ISPs block it. |
| Encryption | Must match the port — STARTTLS for 587, SSL for 465 |
| Authentication | Must be enabled. Use your full email address as the username. |
| Password | Use an App Password if the service requires it (Gmail with 2FA, etc.) |
3. Check If Your Email Is Stuck in the Outbox
Sometimes the email sends but gets stuck. Open your Outbox folder:
- Outlook: Look in the Outbox folder. If an email is stuck, open it, delete any large attachments, and try sending again.
- Thunderbird: Check the Unsent Messages folder under Local Folders.
4. Email Sent But Not Received
If you got no error but the recipient didn't receive the email:
- Ask the recipient to check their spam/junk folder.
- Check if you received a bounce-back message (Non-Delivery Report) in your inbox.
- Send a test email to a different address (like a Gmail account) to see if the issue is with a specific recipient.
- Check if your domain is on an email blacklist at mxtoolbox.com/blacklists.aspx.
5. Emails Going to Spam
If your emails arrive but land in spam:
- Set up SPF, DKIM, and DMARC records for your domain — these are the most effective way to improve deliverability.
- Avoid spam trigger words in your subject line (FREE, URGENT, CLICK HERE, etc.).
- Don't send bulk emails from a regular email account — use a dedicated email marketing service.
- Make sure your sending IP isn't blacklisted.
6. Port 25 Blocked by Your ISP
Many internet service providers block port 25 (the old default SMTP port) to prevent spam. Always use port 587 (STARTTLS) or 465 (SSL) for sending email from a desktop client.