The following steps will guide you through your Thunderbird version 3 profile for Yahoo! Mail to ensure it is configured properly:

Please Note: Some ISPs (Internet service provider) do not permit message routing through another SMTP (Simple Mail Transfer Protocol) server while you are connected to their network. To resolve this problem, replace the SMTP server for the other ISP or the other email account by using the SMTP server that is associated with the ISP that you use to connect to the Internet.

Confirm your email settings:

1. From the "Tools" menu, select Account Settings.
2. Locate your Yahoo! Mail Account on the left column and expand the options by selecting the plus icon.
3. Click Server Settings under your Yahoo! Mail account in the left column.
4. Change "Server Name" to plus.pop.mail.yahoo.com.
5. In the "User Name" field, enter your Yahoo! ID. Please note: Your ID is typically your email address without the "@yahoo.com", however, this rule does not apply to "@ymail.com" or "@rocketmail.com" addresses. If you have either a "@ymail.com" or "@rocketmail.com" address, be sure to enter the entire email address as your ID.
6. Change "Connection security" to SSL/TLS.
7. Click Outgoing Server (SMTP) in the left column.
8. Select the Yahoo! Mail listing for your account and click on the Edit button.
9. Fill out the "Description" as you see fit, such as "My Yahoo! Account."
10. Enter plus.smtp.mail.yahoo.com in the Server Name field.
11. Change "Connection security" to SSL/TLS.
12. In the Authentication method field, select Normal Password.
13. Enter your user name as you did in step 5.
14. Press the OK button to close the SMTP Server dialog box.
15. Press the OK button again to close the Account Settings dialog box.

To ensure the new settings are configured properly, we suggest closing the Thunderbird client and opening it again before sending or receiving messages.

Try alternate POP (Post Office Protocol) and SMTP server names:

If you receive any Authentication issues while using the above server names, you may be able to bypass the issue by using our alternate server names.

To use the alternate server names, use the steps listed above and substitute the following information:

For POP server name: pop.mail.yahoo.com

For SMTP server name: smtp.mail.yahoo.com

Once you have completed the steps, we again suggest closing the Thunderbird client and opening it again before sending or receiving messages.

Examine the configuration of your security software:

Sometimes, a piece of software security (anti-virus, firewall, or anti-spy) on your PC, a piece of networking equipment (router, bridge, or firewall), or your Internet service provider (ISP) may be blocking access to the Yahoo! Mail POP and/or SMTP servers.

Any failure to connect to the Yahoo! POP or SMTP server would normally indicate a network issue.

Try temporarily disabling any security software (such as anti-virus, firewall, or anti-spy) you have installed, as some software security products will actually block the Yahoo! POP or SMTP server or ports. If you are unfamiliar with how to do this, please consult with the software vendor's online help or contact their support services directly.

If you have any network equipment, such as a router, bridge, or hardware firewall, check to see if it is blocking the Yahoo! POP and SMTP servers or ports. If you are unfamiliar with how to do this, please consult the product documentation or the manufacturer's support services directly.

You may also contact your ISP for assistance. Ask if the modem (if provided by your ISP) or software you are using has a firewall feature. It is also possible that the ISP has certain ports blocked on their end.