SMTP (Simple Mail Transfer Protocol) which works in conjunction with POP3 (Post Office Protocol 3) is responsible for sending emails. You will typically encounter an SMTP error through email clients such as Outlook Express, Windows Mail, Windows Live Mail, Outlook, Thunderbird etc. When such email programs are not able to send an email you have composed, they display an SMTP error.
There can be very many causes for the SMTP error you receive and on this page I shall tell you about some of the common ones. This is written primarily for beginners and intermediate level users to help them troubleshoot SMTP problems.
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Sending email error – SMTP
As mentioned, you’ll come across SMTP errors only during the process of sending emails. During the process of setup and configuration of an email account in an email client using Post Office Protocol (POP), you will be asked to provide the settings which would include the incoming (POP) server and outgoing (SMTP) server details.
Outgoing email server address is incorrect
An SMTP error is generated when the outgoing server address is not correct. I suggest you contact the email service for this information and while you are at it, also get the outgoing port number (see below). You can generally find the details of how to configure a new email address in an email client from the company’s web site.
Please read how to change the outgoing mail server for instructions.
The SMTP post used is disabled or not allowed
This is probably the most common cause of an SMTP error. The port specified by your email service is disallowed by the ISP – the company that provides you the internet connection. Typically, port 25 and 26 are disabled by ISPs because of the fear of being abused for spamming purposes. You can generally get around this problem by contacting the Internet Service Provider and asking them for the allowed SMTP outgoing address (yes, this too may change) and the port number. Additionally, you may also need to use a different set of login for it (see below).
SMTP server requires authentication – ISP
As mentioned above, ISPs may disallow certain SMTP ports – 25 and 26. If this is indeed the case for the SMTP error you get, contact the service provider and ask them for the permitted port AND the alternate SMTP address. These new SMTP settings may also require you to log in using a different username and password set – typically, the same of your internet connection. However, always make sure that this is indeed the case.
The outgoing email server address has different username and password than the incoming POP server
On the other hand, the email service (if it’s not the same as the ISP) would require you to use an SMTP login that is different from the incoming POP server. However, this is rare but I have come across it once in my life.
SMTP server uses secure password authentication
Outgoing address, login, port – all are correct and you still get an SMTP error? Ensure you haven’t accidentally missed out on checking the secure password authentication option. You can find it under the email account properties in the email client you use.
Recipient’s email address is not correct
An SMTP error is also generated if the recipient’s email address is not correct and in such cases the email bounces back and is returned to you. How can the email be sent if it does not know where to go, right? Double check the email address to which you are sending the message. There are several reasons why an email can be rejected and I suggest you click on the above link for more details.
Fragile or no internet connection
Lastly, fragile or no internet connection can also lead to SMTP errors. Try opening a web site in browser to confirm if you have an active connection.
