I am a long time Opera user, and in particular I really enjoyed the integrated mail client.
I have managed to successfully migrate all my emails to the "Opera Mail" standalone client released just before they had a massive technology change that forced them to remove many useful features of the browser, including the email client, angering a lot of people, including me.
Opera Mail has never been updated, and this is a big problem because it hangs a lot under Windows 7-10, especially with a large database holding thousands of emails (my opera folder is at 10gb now). One bad click and its window freezes (hangs) to death. After almost two years of crashes this has become unbearable.
So I'm here asking if anybody can recommend a proper replacement for Opera that has at least the UI flexibility of Opera and an integrated email client with a "all unread" email folder that contains emails from all accounts.
I'm aware that the Otter and Vivaldi projects exist, and afaik neither of them has yet implemented a working e-mail client.
I'm also aware that similar behaviors could be replicated by using Firefox/Chrome + a ton of extensions, but I'd rather prefer to have the same tight integration between the browser and email client that is present in Opera 12.x.
Bonus points if it is (natively) portable and has a toggle-able and customizable sidebar.
My hope is to be able to browse the web and read my emails with the same program because that is a workflow I came to enjoy in the past years.