Opera

Opera Mail will by default check mail every five minutes. If you are not connected to the Internet, a message will come up in the Error Console telling you that the mail check failed. This error will typically come up every five minutes when you are not online.

There are two ways to stop this error message from appearing:

1. When you are not connected, tell Opera that you are working offline by selecting File > Work offline
2. Or you can disable the automatic mail check