Why can't I send email?

If your email client receives mail just fine but can't send, the problem is almost always with SMTP configuration. Here's the troubleshooting flow.

Check the basics

1. SMTP server: mail.yourdomain.com.
2. Port: 465 (SSL) or 587 (STARTTLS). Try 465 first; 587 if that fails.
3. Authentication: Required (Yes). Use the same username and password as IMAP.
4. Username: full email address, e.g., you@yourdomain.com.
5. Password: the email account password (not your portal password).
6. Encryption: SSL or STARTTLS — required, not optional.

If any of these is off, sending fails. Double-check each.

"Connection refused" or "Connection timed out"

The most common cause: your ISP or network blocks port 25 (and sometimes 465 or 587).

Many residential ISPs block outgoing port 25 to prevent spam from compromised home computers. Some corporate firewalls block 465. If you can receive but not send, this is often it.

To fix:

• Try a different port. If 465 fails, try 587 (and vice versa).
• Use mobile data to test. If sending works on cellular but not WiFi, your WiFi network is blocking the port.
• Use a VPN to bypass network restrictions.
• Contact your ISP and ask if SMTP ports are blocked.

"Authentication failed"

Wrong password or username. Common mistakes:

• Using just the local part (you instead of you@yourdomain.com). The full email address is required.
• Using your portal password instead of the email account password. They're different.
• Recently changed the password but the email client has the old one cached. Update.

"Recipient address rejected"

You can connect, authenticate, and submit — but the recipient bounces with "550 Recipient address rejected" or similar.

Causes:

• The recipient's email server doesn't trust your domain (SPF/DKIM/DMARC issues). See Email deliverability.
• The recipient is on a strict spam filter (corporate, government, school networks).
• You're being rate-limited — sending too many at once triggers temporary blocks.

For one-off rejections to a specific recipient, ask them to whitelist your address. For widespread rejection, audit your authentication records.

"Relay access denied"

This means SMTP authentication isn't being correctly applied. The receiving server treats your message as spam from an unauthenticated sender.

Fix:

• Make sure SMTP authentication is enabled in your email client. Some clients call it "My outgoing server requires authentication."
• Username/password should match IMAP. If your client has separate fields for incoming and outgoing auth, make sure outgoing is filled in.
• Don't use STARTTLS on port 465 — that's SSL territory. Use STARTTLS only on 587.

"Maximum send rate exceeded"

We rate-limit outgoing mail to prevent abuse:

• Per-account limits (typically 200–500 emails/hour, varies by plan).
• Per-server limits (rare to hit for legitimate use).

If you exceed:

• Wait for the limit window to reset (usually within an hour).
• Spread sends out rather than blasting at once.
• For real bulk sending (newsletters, transactional), use a dedicated email service. See Email deliverability for recommendations.

"Message too large"

Default outgoing message size is around 25–50MB depending on plan. Larger messages bounce.

Fix:

• Compress attachments as a .zip.
• Use a file-sharing service (Dropbox, Google Drive, WeTransfer) and send a link instead.
• Increase message size limit — open a ticket; small bumps are fine, large jumps may not be.

Webmail works but client doesn't

If you can send from the webmail interface but your local client (Apple Mail, Outlook) can't, the problem is client-specific:

• Server settings wrong — re-check using the values in Email server settings.
• Cached old password — update it in the client.
• Local firewall blocking the SMTP port — pause the local firewall briefly to test.
• Antivirus interfering with email scanning — turn off email scanning in the antivirus to test.

Can't send to one specific recipient

If sending to most addresses works but fails to a specific recipient:

• Their server is blocking your domain. Check if you're on a blacklist (mxtoolbox.com).
• Their inbox is full — bounces with "quota exceeded."
• They've blocked your address — you'll see "user unknown" or similar.
• Their domain has changed — e.g., they switched email providers and the old MX records are stale.

Reach out via another channel (phone, in-person) and confirm their email status.

Power-user note

For diagnosing mail flow, our /usr/local/cpanel/bin/showrelays and the cPanel Email → Track Delivery tool show recent send attempts and any failures. The tool is in cPanel under "Email." Each send attempt is logged with the receiving server's response, which is the fastest way to figure out why a specific message bounced.