When I alphatize my e-mails by sender, I can't move page the first page which is only the "Ds"

I have been very busy lately so have over a thousand e-mail-some read and some not read. To read and delete, its easiest for me to have all of my e-mails put into alphabetical order. However, when I do that, I am unable to make it go past the first pages of email. In this particular case, I can't go past the e-mails entitled "dropbox". In other words, it doesn't have a page to do "next page".