When system starts up or wakes up it needs few seconds to establish network connection. At the same time plugin tries to check for new mail and fails as there is no network interface up yet. As a result, error indicator appears and user needs to open plugin's error log window to "clear" error notification. Before that, it isn't possible to be sure that mail checking didn't failed because of wrong credentials or something like that.
I think it is reasonable to make sure that network is up before checking for new mail. Thanks.
Discussion on this issue is already taking place elsewhere.
*** This bug has been marked as a duplicate of bug 4747 ***