Unable to Send Email?

Frustrating, I know.

Being unable to send email can ruin your workday, wreck productivity or even worse cause you to lose out on an important opportunity.

In fact, fixing email delivery issues is one of the top three things we do for our server management customers.

You can save yourself some money by checking these five items first.

• Bad Passwords
• Network Connection Errors
• ISP Blocks & Email Ports
• SMTP Authentication Settings
• SSL Connection Settings

1. Bad Passwords

Never ASSUME, because when you ASSUME, you make an ASS of U and ME. — Jerry Belson

This sounds simple enough but many support tickets we see turn out to be simple password issues.  People complain they are unable to send email and assure us the password is correct.  We reset the password and bang — email is flowing again.

I think the problem often stems from extra spaces.

Firefox and other applications often add a spaces to copy and pasted passwords.  To be certain you are not picking up a space, paste the password to your address or search box  in your web browser.  This is a quick and easy way to verify you’ve copied the password correctly.

When testing why you are unable to send email, just try resetting your password.   That may fix it quickly.

2. Network Connection Errors

Sometimes mail servers crash — not often but I see it happen on WHM/cPanel and Plesk servers.  Simply restarting the service from the control panel often fixes the issue.

Your email client should return a connection error.

Thunderbird error due to an incorrect hostname.

The clue in this message is “mail2.rackaid.com is unknown.” 

This could be a general network issue and you may want to just try again in a few minutes.  If the issue persists, you could have a DNS issue.  If DNS is not working, you will not be able to resolve the domain name.   Of course, it could be something simple – like an incorrectly spelled domain name.

3. ISP Blocking Port 25

Your ISP is blocking port 25.

This is a common issue on customer support desks.  Many ISPs force you to use their own SMTP servers even if you have your own.

U-verse, ATT DSL, and Comcast often block port 25 by default.   I even see this on business accounts.

You can test if port 25 is blocked by using a telnet client to connect to port 25. For example:

This test just sits there until it times out.  If I use SSH to connect to my server then test the port, it works.  I see the SMTP banner.

If you see the STMP banner, then your ISP (or firewall) is blocking the connection.

One tip is to use port 587. Many ISPs do not block this port:

If that still fails, call your network provider.  On most business accounts, the will permit port 25.  Increasingly, residential accounts are permanently blocked and you will be unable to send email except via your providers SMTP services.

For reference, here are the key email ports to keep in mind:

• IMAP 443
• IMAP over SSL 993
• POP3 110
• POP3 over SSL 995
• SMTP 25
• SMTP over SSL 465
• SMTP Submission Port 587

4. SMTP Authentication

Most SMTP server require a valid username and login to send email.  If your SMTP authentication settings are incorrect, you will be unable to send email.

Server rejects the email with relay denied. This likely means SMTP authentication is not enabled.

If you get a relay denied error and your password is correct, then SMTP authentications is likely not correct.

If your password fails after resetting, make sure you are using a valid authentication method.  Most email clients support a variety of authentication methods such as:

• Normal or Plain Password
• Encrypted Password
• Kerberos

Most systems support normal/plain as well as encrypted passwords.  In most cases, you should see an error about  “authentication methods” if this is the problem.

Password encryption and SSL settings are often confused.

SSL encrypts the network connection.  Password encryption avoids sending your password in plain text.

If you are using SSL encryption, you often do not need to use password encryption.

5. SSL Connection Settings

For security, many email service providers now require you to connect to SMTP over a secure connection. SMTPS or secure SMTP uses SSL to secure the network connection between your email client and the server.  I recommend all email communications be sent over SMTPS.

In MS Outlook, you may need to select “This server requires a secure connection.”   There’s similar options in other email clients.

In addition to making this setting, some servers may require you to connect on port 465 instead of port 25.  Port 465 is reserved for SMTP connections over SSL.  If port 25 and port 465 fail, try port 587.  Port 587 is the mail submission port.