A recently downloaded e-mail is no longer visible in the inbox although a search for the sender finds the e-mail and says that it is in the inbox.

As background, I recently migrated to Thunderbird and imported a very large number of e-mails. The issue, however, is in regard to a new e-mail that was downloaded yesterday. The new e-mail was downloaded in a normal fashion, but when I went to look for the e-mail in the Inbox, it was no longer visible in the (although I had not moved it or deleted it). Running a search on the sender's name finds the e-mail. It is in a thread of 6 or 7 e-mails. The search shows the e-mail is located in the Inbox, however a sort by sender name in the Inbox does not reveal the e-mail. In the search result, I starred the e-mail (it is the only starred e-mail in my e-mail database), but a search of all my e-mail folders shows no starred e-mails at all. I also went through all my folders and moved all e-mails into the "read" status, then found the lost e-mail using the search function and marked it as unread. The Inbox folder shows that I have one unread e-mail in the folder, however when I filter for unread e-mails, the results are zero.