Messages not marked as readed

[xstable]

If I read I read my messages on my pc E-Mail Client named: Thunderbird, the message is marked as read in those clients.
But if I open my k9 email client they are still marked as new messages how can I fix this

[OldieAB]

Has the folder sync’d? If you pull down, the arrow spins, then are the emails marked read?

If so, you likely need to sync more at the cost of phone battery.

[xstable]

No, they are not changed after sync. That was the first thing I’ve tried

[Epsilon555]

[Hamburger Menu] → [Gear Icon] → [Account] → [Read Mail] → [Read When Opened] ← check button here.

Is this option enabled?

[xstable]

The problem is not to mark it as readed in k9, the issue is that it’s not synchronized. … no matter on which device it was read.

[Epsilon555]

Go to [hamburger menu]>[Manage Folders]>[Enable Synchronization] option for all folders.
This is how K9 synchronization is set up.
You can also enable the option to synchronize folders with fetch in the other menus.