Up until recently it has been near impossible to access Yahoo IMAP through any client that wasn’t the Zimbra Client, or else a device like a Blackberry or Apple iPhone etc. Zimbra sends a special command to the Yahoo IMAP servers which authenticate it as an allowed client. I had been using a modified version of Thunderbird that sent this command also, as I prefer the interface and search in Thunderbird.
However it now seems that Yahoo have allowed access to their IMAP servers without this command, and as a result all clients should be able to connect now. I have set up my unmodified Thunderbird on my Ubuntu laptop to connect and it worked fine. I also tried Outlook to see if it worked, and it worked without a hitch. One thing however that is not clear is whether or not this is temporary or whether Yahoo are now offering it free to all users. It is possibly part of their plans to become more competitive in the Webmail market, after having suffered a 10% loss in the number of users in the last year to rival services. This has made it the second largest behind Microsoft’s Windows Live Mail. Google has had a 21% increase in the number of users, and they of course offer IMAP access.
Incoming Server Settings IMAP Server: imap.mail.yahoo.com IMAP Port: 993 IMAP security: SSL/TLS Outgoing Server Settings SMTP Server: smtp.mail.yahoo.com SMTP Port: 465 SMTP security: SSL/TLS
The SMTP requires authentication, the same username and password you use to authenticate to the IMAP server.
I find that if your email address is firstname.lastname@example.org then user will work as your username, but I have not tried the full email as the username.