If you’ve had your Gmail account for years, there’s a good chance that you have thousands of unread messages. If you’re close to using up your 15GB of free storage, you’ve probably tried to delete some spammy emails or unsubscribe to those…
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https://www.cnet.com/tech/services-and-software/gmail-full-how-to-get-15gb-more-data-without-losing-any-messages/