I cannot receive mail from a family member today.

[rufusfrog]

The error code he receives is TT406 which seems to say the emails have been rejected as suspected Spam. He is using a gmail.com email address to send to my TalkTalk address. I know it is not Spam.

[Gondola]

It's not your relative's email address that's the source of the problem. It's that the same outgoing mail server that was sending your relative's email is shared with many other Gmail addresses and some of these are sending large quantities of spam to TalkTalk Mail users. So, TalkTalk has blocked the Gmail outgoing mail server to send a strong message to Gmail that they need to stop the spam at source.

Spammers will eventually give up trying. The natural evolution of cases like this is that spam will be reduced, the mail sender reputation will be improved, the hard block will come off, rate limiting may be applied and then when sender reputation is proved all limits will be removed.  Often, Gmail will start using a new sending IP address that has a better reputation and no block. Either way, given time, your relative will find the email will flow freely once more.

If they don't wish to use a proven workaround in the meantime then patience is the solution. Don't expect TalkTalk to whitelist specific email addresses as that would have to be offered to all and manually whitelisting is not only a time consuming solution it's an open door to spam from Gmail accounts that are whitelisted and then hacked.

[rufusfrog]

Having to mail via a third party the whole time is not a workable solution! I have put the sending email address in my private notes area (as requested by @Ady-TalkTalk on similar threads). My relative is not a spammer nor has he ever (to his knowledge) had his email address spoofed by a spammer.

[Gondola]

OK, it was fortunate that the Google Mail worked. The TT406 rejection usually is detection of a 'spammy' IP address. So, I'd say that TalkTalk is flagging up one (but maybe more) Gmail sender IP address(es) that have been detected as sending spam. So it's not a total block of the gmail.com domain, that was happening a while back, but a specific rejection of an IP address.

Gmail does have a lot of IP addresses at its disposal so hopefully they can take 'spammy' IP addresses temporarily (and spam sending mailboxes permanently) out of service. That's the usual resolution. 

In the meantime, just use whatever workaround is best for you both.

[rufusfrog]

Hi Gondola. He has tried twice - both plain text messages (the second one very plain as a test!). He forwarded the first message to his partner and she was able to forward it to me from her Google email account so it doesn't appear to be anything to do with the contents.

[Gondola]

Hi @rufusfrog 

You're right that TalkTalk is reporting that it has detected outgoing emails as spam being sent from the Gmail sender. This doesn't mean that your family member is sending spam but it does mean that the Gmail server has and as a result TalkTalk is not willing to accept delivery. 

Just as a precaution it would be worth your family member double checking their device to make sure it is clear of viruses and malware that may just be adding some suspect content to the outgoing mail message. After that try again but with a simple text message, no attachments.