The Feedburner team released a system update announcement, that the email subscription service will be discontinued in July 2021.
FeedBurner has been a part of Google for almost 14 years, and we’re making several upcoming changes to support the product’s next chapter.
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Starting in July, we are transitioning FeedBurner onto a more stable, modern infrastructure. This will keep the product up and running for all users, but it also means that we will be turning down most non-core feed management features, including email subscriptions, at that time.
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we recommend downloading your email subscribers so that you can migrate to a new email subscription service.
You can read about these changes on the google website.