Finally got fed up when faced with how to delete 9,000 of 10,000+ email message using mutt in linux. The key is to get the messages tagged. To tag messages, hit “T” (capital T). Then, you will be presented a “Tag messages matching:” prompt.

Tag the messages by date:

Tag messages matching: ~d dd/mm/yyyy–dd/mm/yyyy

For example:

Tag messages matching: ~d 01/01/2012-31/12/2012

Tagged messages will now have an “*” (asterik).

Delete all the tagged messages:
Hit the “;” (semi-colon). You will have a “tag-” prompt. Then, just hit “d”.