The popular POP3 email protocol is sometimes regarded as inconvenient because of the following shortcomings:
If you switch your email client from POP3 to IMAP, you will be able to handle your emails using your email client, a browser and a mobile app at the same time. In this case your emails will not be marked as read and will not disappear from the Yandex.Mail server.
If all emails are there, mark them as read. To do this, go to the Folders and Labels section, select each folder one-by-one, and click on the Mark all messages in folder as read link (to the right of the folder list).
If any emails are missing on the website, but they are still in your email program, they can be uploaded to the website using the IMAP protocol. Find the emails in the email program which are not available on the website, select them in the list and drag them to the Inbox folder, or any other folder in the new account.
Select your computer's operating system and email client for further instructions.