Fix common problems when email is not sent

When encountering email errors when sending, you should carefully read the details of the error messages included in the email to find solutions.The following article will help you fix some of the most common errors.

1. Wrong email address

It can be said that this is the most common error today. An email address usually consists of two parts: username ( username ) before the @ character and the domain (domain) after the @ character. So if you send an email to a bogus address, you will immediately see an email returned with a message like the username does not exist on this system or DNS Error: domain name for found (name wrong domain. Besides, most users often confuse two addresses @ yahoo.com and @ yahoo.com.vn , @ hotmail.com and @ hotmail.com.vn ; or characters l , 1 and I.

2. The recipient mailbox is full

Another reason may be because the recipient's mailbox is full with an error message that is usually mailbox is full or quota has been exceeded. If you send an email with a file attached to the above case, you should try sending the email again without attaching a file to notify the recipient of the status. Otherwise, you can do nothing but call or use another method to let people know about their mailbox status.

3. Your IP address is locked

For example, see the following message when sending messages in Gmail:

554 554 5.7.1 Service unavailable;
Client host [74.125.82.47] blocked using dnsbl.sorbs.net;
Currently Sending Spam See: http://www.sorbs.net/lookup.shtml?74.125.82.47 (state 14).

Blocking IP is one of the best ways to prevent spam, but if your IP is unfortunately on this list for many different reasons, it is unjust. In this case, please resend the email and use a different IP address. You can check if your IP address is blacklisted by visiting http://www.aboutmyip.com/AboutMyXApp/BlackListCheck.jsp or http://multirbl.valli.org. If you see that it appears from FAILED next to a server, all IPs using this server are blocked. Changing one location to another can overcome this situation. In addition, you should install an antivirus program because it is simple if your computer is infected with the virus, it will likely become a spam or malicious distribution tool for bad guys and will be blocked by servers.

4. Network connection error

Sometimes the mail server fails, has occurred on WHM / cPanel and Plesk servers. The fix is ​​very simple, just restart the server from Control Panel.

When an email cannot be sent, your mail application will return the following error message:

The clue to solve the problem is in the ' mail2.rackaid.com is unknown ' error message. This may be a general network problem and you can try again in a few minutes. If the problem continues, you may experience DNS problems. If DNS does not work, you cannot resolve the domain name.

See also: Some troubleshooting tips for internet connection

5. ISP blocks port 25

This is a common problem because many service providers force you to use their SMTP server even when you have your own server. You can check if port 25 is blocked by using the Telnet application to connect to port 25.

For example:

If using SSH to connect to the server to check the port.

If you see TMP then it means that the network service provider (ISP) (or firewall) is blocking the connection. The trick to fixing this problem is to use port 587. Many ISPs do not block this port:

If it still fails, call your network provider.

For reference, here are the main email gateways to note:

1. IMAP 443
2. IMAP over SSL 993
3. POP3 110
4. POP3 over SSL 995
5. SMTP 25
6. SMTP over SSL 465
7. SMTP Submission Port 587

6. SMTP authentication

Most SMTP servers require a valid username and login to send email. If your SMTP authentication settings are incorrect, you will not be able to send email.

If there is a Relay denied error but the password is correct, you may be having incorrect SMTP authentication issues. Please check SMTP authentication again.

Security of password and network security authentication are two different settings, both of which must be accurate. After resetting the password and still being unable to send the email, make sure you are using a valid authentication method. Most email applications support many different authentication methods such as:

1. Normal password or pure password
2. Password is encrypted
3. Kerberos

Most systems support normal / simple passwords as well as encrypted passwords. In most cases, you will see an error on the 'authentication method' if a problem occurs.

Password encryption and SSL settings are often confused. SSL encrypts the network connection while encrypting the password in order to avoid sending your password in plain text. If you are using SSL encryption, you do not need to use password encryption.

7. Install SSL connection

For security, many email service providers require you to connect to SMTP via a secure connection. Secure SMTPS or SMTP uses SSL to secure the network connection between your email application and your server. You should set up all email communications sent via SMTPS.

In MS Outlook, select the option "this server requires a secure connection". And in other email applications also have the same option.

In addition to performing this installation, some servers may require you to connect on port 465 instead of port 25. Port 465 is reserved for connecting SMTP over SSL. If port 25 and port 465 cannot be used, try port 587, this is the mailing port.

8. When not having any error messages

This is the most difficult cause to handle. You have confirmed that the email address you sent is correct, most likely some anti-spam rules are taken by the server administrator who filtered your email into this list. This may be based on IP (as above) or based on some content in your email such as some images, phone numbers, or other text. Unfortunately this does not leave an error message when you send an email. Therefore you can temporarily use another email address to send. If the mailbox is in use, it is extremely important for you to contact the mail service provider like Google and Yahoo to fix it.

If using email provided from Internet service providers, contact their customer support service. They may ask for a sample of the emails you are trying to send along with the error messages or codes you received. Be sure to give them whatever they need to help resolve your situation thoroughly.

See more:

1. Learn about how email works
2. 25 most common errors for email security
3. Introduction to Email technology