Certain email companies and internet-based companies operate using IPV4, an almost outdated internet protocol. If you are not sure what internet protocol a website is using, you can always check by clicking on the "information" link on the bottom of a page or by opening web source information with a right click on your mouse and then clicking on "view web page source." This should tell you if a company is using IPV4 or IPV6. If you are wondering why anyone would continue to use an older version of web protocol, here are a few reasons for it.
IPV4 Market Price
As with any form of technology, or any technology product or service, the older it is, the cheaper it is. IPV4 use in many cases is significantly less costly to run than the new IPV6, which reduces company operation costs overall, especially for internet-based companies like Yahoo Mail. When costs are kept low, these companies can offer free or reduced price services to consumers, thereby increasing the number of consumers who use the service(s) and increasing profits and/or product usage. For businesses that are just starting up and using an internet-only approach, IPV4 is the way to go because it will not break your budget.
IPV4 Is Less Complicated to Use
Many internet-based companies like the fact that IPV4 has shorter web addresses. They are limited to 32-bits, rather than the 40+bits of addresses for IPV6. This saves web address developers time and money in creating IP addresses for consumers, and limits the number of addresses that can be consumed by a single customer. Shorter web addresses also help sites load faster, and are frequently more compatible with older computer software.
IPV4 to IPV6 May Require Web Design Overhaul
Since many website designers base their products on IPV4 protocol while building websites for clients, upgrading to IPV6 could result in a total web design overhaul. Most companies do not have the time or the money to wait for new sites to be completely rebuilt from scratch, launched, tested and debugged. As the result, companies stick with what they have, because "if it is not broken, do not fix it." With a vast majority of other companies in the same boat and taking the same approach to their websites and their protocol use of IPV4, it just makes sense to keep things as they are and use "patches" for any connections to companies that have upgraded to IPV6.