''The folder Inbox is full, and can't hold any more messages. To make room for more messages, delete any old or unwanted mail and compact the folder. '' This is a very clear message. The Inbox should be used as an Inbox for new incoming mail and not used as a general store. Each Folder displayed in the Folder Pane is actually an mbox file, with emails written one after the other in the order they were downloaded. So you are currently storing all those emails in one single file which must be rather large to get that message. '''Do this to resolve the situation:''' * Create some folders with suitable names to organise your emails. eg: 'Family', 'Friends', 'Clients, 'Thunderbird', 'Online Orders', 'Bills' etc. * Then move emails from Inbox into the appropriate folder(s). * Delete any emails you do not want. * When Inbox is empty, right click on Inbox folder and select 'compact'. When compacting is finished, click on 'GetMail'.