I have windows 7 premium, 64 bit OS

Since Microsoft switched my e-mail: (removed PII) to Outlook.com server, I am losing some important e-mails on my computer.
I still have those e-mails on my smartphone, which has Hotmail installed.
Last incident happened today: I lost one e-mail from two different messages posted me by the same sender.

Will you please let me know how can I fix this problem or how can I switch my e-mail account back to Hotmail on the computer.

Thanks

Alex Rysin