Cannot Send Email: How to fix Email Sending and Receiving Errors
Posted by Jeffrey Huckaby 10/17/2006
Being unable to send email is one of the most common complaints we receive in providing help with dedicated servers. Doing a little detective work can save you a lot of extra hassle. If you’re having trouble sending email from clients like Outlook, Eudora and other POP3/IMAP software, please check the following issues:
Verify that all password information is correct. We get many requests that simply turn out to be a password error. When cutting and pasting be sure to watch out for extra spaces.
Mail Server (SMTP) is Offline
Your server could be running and serving both POP3/IMAP but not providing SMTP service. On many systems, the program responsible for POP3/IMAP is not the same as the one for SMTP. As a result, you may be able to check mail but not send. Try restarting your server or email service from your control panel.
An increasing number of ISP’s are blocking port 25, the port used to send email. Many of the major ISP’s, including NetZero, MSN, Earthlink, AT&T, Comcast and Verizon, block port 25 in an attempt to control spam. If your ISP blocks port 25, then you will be unable to send email out of your server. This is not a server problem but a direct block by your ISP. We can often work around these blocks by configuring your mail server to listen to additional ports.
You can test if port 25 is blocked by using a telnet client to connect to port 25. If you connect successfully to port 25, you will see your mail server’s banner. This will list some information about your mail server. If you cannot connect to port 25, then either your mail server is down or your ISP has block port 25.
ISP blocks are becoming an increasing problem. Generally, once password issues have been ruled out, sending email is all or none. If the mail server is down, no one will be able to send email. ISP blocks will only impact those clients behind that ISP’s network.
Server Load Throttling
Many SMTP servers will begin to reject email if server loads are too high. If you have root access, you may want to login and run “uptime”. This will tell you your current load averages. Many systems stop responding to email requests if loads exceed 12 for a five-minute period. If the load does not decline to below 4 within a few minutes, then you may have a service performance issue.
Most email servers use one of two mechanisms to determine if a user is permitted to send email.
The first method, “POP before SMTP”, requires that the user first check their email before they can send. If a user cannot check their email, then they will not be able to send. Try restarting your POP3/IMAP server and testing again.
The second and preferred method is called SMTP Authentication. This method should be used if your system supports it. Current Ensim, Plesk and cPanel servers all support SMTP AUTH. To use this feature, the user must check configure their email client to use authentication for sending mail. In Microsoft Outlook, there is a check box called “This server requires authentication.” That box should be checked.
If the above items do not seem to be the cause, then you may have a mail server configuration issue. If you need someone to help you with your server, just let us know.
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