"The folder Inbox is full, and can't hold any more messages" error
You may see the following error message:
"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."
The error may appear if your inbox file has exceeded the memory size limit. When using a POP3 account, Postbox stores each folder in an individual file. On some operating systems, there is a memory size limit near 4GB. You will see the above message when the Postbox file storing your inbox reaches around 4GB.
How to Fix It
Compact your folders
When you delete a message, it doesn’t really get deleted from the folder. It gets marked as deleted. Postbox sees that marking, and knows not to display the message. Compacting a folder will command Postbox to remove all messages marked as deleted from that folder.
- Right-click on the folder.
- Select Compact.
Switch to IMAP
If possible, switch from using a POP3 account to IMAP, where messages do not need to be stored on your computer. For instructions, see How to Convert a POP Account to IMAP