How are you trying to access your pipex mailbox? Webmail via an Internet browser or using email client software / email app?
Are you using the master pipex email address or an alias email address? The mailbox is for the master email address which is of the form abc12@dsl.pipex.com whilst an alias uses a more user friendly address of the form firstname.lastname@dsl.pipex.com but inbound emails for linked aliases always go to the master mailbox.
Do you know the password?
Select here: Sign in to TalkTalk Mail
Enter your full TalkTalk Mail pipex email address, select Continue and enter the password, select Sign in.
Do you get signed in? If not, what's the error message or what you see?
