“Some incoming emails are being delivered directly into a folder called Notes instead of Inbox. The problem occurs in TalkTalk Webmail itself, not just on my devices. There are no mail filters or rules configured.”
This will require TalkTalk to deal with your problem. There are no TalkTalk support staff on this forum anymore.
Please see my signature for TalkTalk contact methods.
The TalkTalk Community has now moved to a peer-to-peer support model. This means that the TalkTalk team will no longer be here to support with queries. Don’t worry, there are plenty of ways to reach out if you need to speak to TalkTalk directly. For more details check out the link here How to contact TalkTalk Broadband - TalkTalk Help & Support. NB. Online Chat is now available after logging into MyAccount.
