While working offline, you cannot move or copy messages that were not downloaded for offline use. From the Mail window, open the File menu, choose Offline, then uncheck Work Offline, and then try again.
Mjaztym až offline źěłaśo, njamóžośo powěsći pśesunuś abo kopěrowaś, kótarež njejsu za wužywanje offline zesěgnjone. Pśejźćo we postowem woknje do menija Dataja, wubjeŕśo Offline a pótom Offline źěłaś a wopytajśo pótom hyšći raz.