Often web hosts get contacted by account owners who are unable to send or receive emails via Outlook. The error message they see in their Outlook would be:

Task 'account@domain.com - Sending' reported error (0x80042109) :  "Outlook cannot connect to your outgoing (SMTP) e-mail server. If you continue to receive this message, contact your server administrator or internet service provider (ISP)."

In our role as Website Support for web hosting companies, this is a concern we quickly resolve for users who have email accounts hosted in the customers’ servers. 

As a one-size-fit-all solution is not possible for this error, today we’ll see what are the common causes for this error and how we resolve them for the customers.

 

What causes ‘Outlook cannot connect to SMTP server’ error

The SMTP error in Outlook can happen due to many reasons, broadly classified into these categories – 1. User end issues 2. ISP issues 3. Server side issues.

1. PC/Laptop firewall issues

Though not so common, third party firewalls and anti-virus software in user PCs can block connection to certain IP ranges, which could include the server IP as well. This can give errors while connecting to the mail server for sending or receiving mails.

To check the connectivity issues from user’s PC or laptop to the mail server, we get the results of ‘telnet domain.com 25’ from the users, which shows whether the user is able to connect to the SMTP port in the mail server.

2. Outlook configuration mistakes

Most common reason for ‘Outlook cannot connect to SMTP server’ error is the wrong configuration settings of Outlook. This happens especially in the case of newly configured email accounts.

A mis-spelled mail server name to a wrong port setting in Outlook can cause connectivity issues to the mail server and end up giving error while trying to send or receive mails.

By default, the port settings for mail related services are these, and a connection problem to these ports can lead to Outlook error:

SMTP - port 25 / 587
POP3 - port 110
IMAP - port 143
Secure SMTP (SSMTP) - port 465
IMAP4 over SSL (IMAPS) - port 993
Secure POP3 (SSL-POP) - port 995

There are also chances that some web masters may have duplicate profiles in Outlook, which will have an old mail server configured in it, and therefore would be trying to connect to the wrong mail server.

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3. ISP firewall issues

Some ISPs are known to block traffic through port 25 to minimize automated spam. This is the most common reason for Outlook error 0x80042109 ( ‘Outlook cannot connect to SMTP server’ ).

A ‘traceroute’ result to the mail server from the user end helps to reveal if there are any connectivity issues in any of the intermediate network between user PC and mail server.

4. Server firewall issues

Firewalls are the security barriers which we setup in servers to protect them from malicious attacks or hacks. Occasionally, these server firewalls can block certain IPs or IP ranges based on any anomalous behavior.

For instance, exceeding the login failure attempts or too many connection attempts to the server can lead to an IP address being blocked in the server firewall. This can lead to error ‘Outlook cannot connect to SMTP server’.

The above were some common reasons for Outlook error 0x80042109. In our website support services, we treat each customer as unique, and explore all possibilities before giving a final solution.

How we resolve ‘Outlook cannot connect to SMTP server’ error

We follow a unique step-by-step debugging process to resolve the Outlook error 0x80042109 for the customers, in minimal time.

1. Resolving client end issues

When a user reports the error, we check the server logs to see if the user is able to establish a connection successfully to the mail server via webmail or other mail clients.

If the user can successfully connect to mail server IP and ports for SMTP and POP, then the issue is with the Outlook settings and not connectivity problem. We verify this using ‘telnet’ and ‘traceroute’ results.

We then assist users with the correct steps to configure their Outlook mail client, with the port number, SSL settings and mail servers to be used.

 

outlook-cannot-connect-to-smtp-server

Outlook SMTP configuration

2. Resolving ISP or network issues

For ISP or network connectivity issues, we suggest alternate methods to the users to connect to the mail server and send mails.

To override ISP port blocks and to enable users to send mails, we usually configure SMTP on a different port in our servers. Using a non-standard port such as 587 also helps to secure our email server.

Once the mail server is configured to listen to the new port, we also add this port to the firewall white-list to allow incoming connections to that port.

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3. Resolving server side blocks

Looking for the customer’s IP in the server’s firewall is one of the first things we do when we don’t see a recent connection on other service logs. User’s IP addresses can be identified using tools such as ‘http://whatismyipaddress.com/’

Once the IP is found to be listed in the firewall, we immediately unblock it to establish connectivity for the customer. There are different types of firewall such as CSF, iptables, etc. and the de-listing method varies in each.

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As recurrent IP blocks can lead to discomfort and loss of time and effort for the end users, we strive to reduce the inconvenience caused to customers with these pro-active steps:

  1. Regularly auditing the server logs to examine IP blocks and unblock valid IPs.
  2. White-listing IP addresses of customers after verification.
  3. Setting custom firewall rules for customers to prevent discomfort but avoid misuse.

If you’d like to know how to provide a delightful customer support experience to your email users, we’d be happy to talk to you.