How to Set "Hide these messages from other views" for a Gmail IMAP Folder View

With IMAP folders, you can't right-click on them, goto properties, then options and check "hide these messages from other views" so that its messages are controlled by the "show hidden" option in other views like you can with labels. But, since IMAP folder views are very similar to other views and labels, the option is supported for IMAP folders too. It's just not exposed to the user.

To control this option for IMAP folders, you need to take note of the IMAP folder's name, close down Opera and edit index.ini in the mail folder. You need to find the index for the IMAP folder. You can do this by searching for its name. Just note that there might be more than one index with the same name so you have to make sure you get the right one.

Once you find the right index for the IMAP folder, you need to change its Flags= line to a different value. This page will help you with that. Set the page to the existing number in index.ini. Then, check the "hide from other" checkbox to get the number you need. Then, change Flags= to that number and save your changes. Just note the page might become outdated after a while, so use at your own risk and backup index.ini first.

By default, most Gmail IMAP folders have "hide these messages from other views" set so you don't see duplicates in Opera's views (unless you have "show hidden" checked and "show duplicates" checked for those views). But, because of a bug in Opera, "[Gmail]/Important" and newly-created IMAP folders that represent Gmail labels won't have "Hide these messages from other views" set, which will cause you to see the messages from those folders in other views. To fix those IMAP folders, fix their Flags= line as mentioned above. As a shortcut, Gmail IMAP folders that don't need fixed usually have Flags=263 and ones that need fixed have Flags=259. But, note that some Gmail IMAP folders like "All Mail" shouldn't be messed with.

Note: Although you can do this stuff with regular IMAP accounts, there's no reason to.