Mac Mail stuck at 'downloading messages' - with excessive number of messages

By way of preface I should say I have Googled several search terms and looked on Dreamhost's own help pages - there may be a fix for this I have overlooked and if so apologies.

Currently the inbox for one of my mailboxes (of the five I host at DH) is stuck at 'downloading messages.' the number is excessive - I doubt I got 2600 emails since yesterday afternoon. That said I am certainly getting lots and lots of messages since this is the account I use for shopping and every retailer on earth is sending 'sale' messages this week.

Seems like there was a way to re set the email count itself with another provider I used to use but I cannot remember details. Any suggestions appreciated.