Hi JohnTa
I assume your son is using a gmx.co.uk domain address. Is that right? I've checked that the gmx mail is sent fully authenticated, that there's a DMARC quarantine policy in place and that the domain is not on any of the usual spam blacklists.
I also assume that the mail is being sent direct to your TalkTalk address and not via any intermediate mail forwarding service. Is that right? If mail was being forwarded then the GMX DMARC quarantine policy would tell TalkTalk to put the mail into the Spam folder.
Let's assume that for whatever reason the mail is delivered to the Spam folder then the fix is to log into TalkTalk Mail webmail and select the message in the Spam folder and then select from the toolbar Not spam. This should then notify network filtering that future mail should be delivered to the Inbox assuming that it's TalkTalk's CloudMark network filtering that was tagging the mail as suspect spam.
Select here: Sign in to TalkTalk Mail
Enter your full TalkTalk Mail email address, select Continue and enter the password, select Sign in. Selecting the message in Spam and marking as Not spam will move that message to the Inbox.
Let us know if that effects a full time fix.
