Good to know you can access TalkTalk Mail on your Samsung tablet which gives you confidence that your mailbox is working.
What is the iMac OS version? And which Internet browser version are you using? Is it Safari, Chrome, Edge and is it fully updated?
Are you using a VPN that may be part of an Internet security package or Ad blocker / cookie blocker software? TalkTalk Mail does require cookies to be retained.
If the OS is up to date and the browser is up to date have you carried out a browser reset / cleared browser cache and cookies to remove any corrupt pages or cookie downloads?
