Today when I start KMail, my Gmail account becomes offline. Even I connected to internet and I try to refresh folders, it is still offline. I also click some links like: Account is currently in offline mode. Click here to go online . . . But it doesn't work. I try to restart KMail but my Gmail account is still offline. I cannot read any emails.
Solved. It is just the reason of unstable network. If I change to a better WiFi or wired network, the Gmail account goes back to online. The troulbesome WiFi is shared from my smart phone (4G LTE).