• Your emails are either stored on the server of your email provider or on your phone, depending on your preferences. If you use IMAP, your emails are solely stored on the server. Email messages, on the other hand, are downloaded and saved on your phone using POP3 settings.
• There is no single server that stores all of the email addresses. Every email address is kept on their server. Gmail addresses, for example, are stored on Google servers, whereas Outlook emails are stored on Microsoft servers.
• Your emails and folders are synced with Outlook, which saves them in a local cache file on your computer. A pst-file is used to store your mail cache. An ost-file is used to keep your mail cache. 

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