Unable to receive mail

[shortchoes53]

I can send, but unable to receive.
Outlook 2003 - unable to Receive e-mail Error (0x8004210E) Mailbox is
temporarily unavailable because another e-mail message is being delivered or
another mail application is accessing it Server Responded ERR Box Locked.

 

[Roady [MVP]]

That is an error given by your ISP. How long do you have this error already?
If you have a virus scanner that integrates with Outlook disable this
integration and try again.