We're seeing a few TalkTalk Consumer customers using legacy mail domains that are not receiving mail messages because their email client software is still using out of date (not recognised) legacy server host name and maybe insecure port settings. The email client software / app requires updating to replace the out of date settings.
On updating the email software incoming, outgoing and some advanced server settings, you'll possibly be asked to accept a new certificate (yes, accept) and to enter the email password so have the current password ready. Tick to save the password before entering it.
Supported* email client and app settings are:
IMAP (recommended) or POP3
Full email address
Incoming mail server
Incoming Port (IMAP / POP3)
993 / 995
Incoming Connection Security
SSL/TLS (Use SSL on for mobile)
Outgoing mail server
Outgoing Connection Security
STARTTLS (Use SSL on for mobile)
Outgoing Authentication Required
Apple/Mac Mail Connection Security is use TLS/SSL
It's also important to make sure the email address is added to a TalkTalk Consumer customer MyAccount to avoid restriction to webmail only access and possible deletion.