That sounds like the emails are marked as deleted on the mail server.

Right click the account in the folder pane, select settings and make sure the server setting show deleted mail is not displayed with a strike-through.

Do you have any Message Filter that is set to delete any email?

Please check all message filters, you may have a filter set up incorrectly, so it is marking all incoming mail as deleted. Combined with an account setting > server setting to 'just mark it as deleted' will show deleted mail with a strikethrough.

Matt; Toad-Hall -

Have no message filters as yet on thunderbird and all account/server setting were set to not delete any mail. kody.b

Do you ever use a phone or another computer to see emails?

Can you still see all those marked as deleted emails still in the webmail Inbox when you access the webmail account via a browser? Is there any indication those emails have been forwarded?

Do you have a set up on server where you have emails being forwarded from eg: a godaddy account to a gmail account ?

Check the webmail account itself is not set up to auto forward anything.

What server do you use ? Comcast. Outlook. Gmail etc ?