As many of you know, Opera stopped using the Presto engine, and is using Chrome's engine instead. Maybe that was why they decided to remove the mail client to be its own standalone program. That's a good thing.
I use Opera a lot, all day, with many, many tabs open. I also usually have a stylesheet editor open, a FTP client open, a web editor open (HTML Kit Tools), probably an image editor, maybe a color palette saver, and an Open Office document because I don't like Word and clients like to send me formatted stuff even though I repeatedly ask for plain text. With the Presto engine, there was only one process, and it sometimes could eat up a lot of memory. I get a lot of Opera (not responding) because of all the programs I have running, and Opera is checking the mail, too.
With the Chrome engine, Opera uses more processes, and is even hungrier. As I wrote in Just Say No to Opera 15 Upgrade, there are just too many features missing from Opera 15. So, my only choice is to stay with Opera 12. I went to Opera's website today, and noticed that there is a link that says "Looking for the previous version? Download Opera 12". I guess the folks at Opera have figured out that there are too many people who don't want that abortion of a browser, the "new" Chrome in Opera's clothing.
This lead me to a dilemma I solved today. Opera 12 uses memory because it's always checking for mail, and I don't want to "upgrade". So, I downloaded Opera Mail and installed it.
What a pleasure! Opera Mail was nice enough to import almost all my mail accounts and messages from Opera 12. There were two accounts that I had to add manually, took five seconds. All my subfolders and labels came in fine, and it's nice and fast – I guess because it's still running on Presto! Then I told Opera 12 not to automatically check mail for the accounts. When I am satisfied that everything is working perfectly, I will just delete the mail accounts from Opera 12 completely.
So, there you have it, the best of both of worlds. Enjoy!