Bell Webmail Support.

As a workaround, you can delete your inbox.dat file from the webmail directory before launching the mail client and then re-create your mailbox over the internet by going to www.bellcanada.com/activatebellwebmail. It may take a few minutes for this process to complete after which time you should be able to launch your e-mail client. Once complete, it may be necessary to delete all of the contents from your Inbox and Sent folders before re-starting the e-mail client if you still have issues with launching it successfully.

Must Read: Bell Webmail

The inbox.dat file is a hidden file that contains locally cached copies of all mails for faster access, if this gets corrupt it will cause delays and problems with loading mails.