(22nd November 2015)
There have been several instances of issues sending mail into the following domain names which I think all fall under the Talk Talk group of companies. I have seen another mail rejected message this morning to a talktalk.net recipient.
Each time I see these problems or someone reports a mail rejected message I get in contact with the sending hosting company and ask them to check. They report back that the issue lies with Talk Talk.
There seems to be some evidence that this group of domains have tightened up their security with regards to email. It has progressively got more and more complicated this year, most likely because of the high volumes of emails being sent by spammers. Various checks are being carried out to ensure that the server associated with a domain is really where the mail came from, and not from a 3rd party.
If you see any rejection notices and your mail is based on your domain name, please forward them to me so I can look into the reason why it is being rejected.
There are two common mechanisms, one is Black Listing; this means that spam has been detected as originating from the server, so all mail from that server is blocked. These generally last for a few hours before they are cleared. The hosting companies we use are usually very quick to detect this and take action. They also have checks on mails being sent from the server to detect and stop spam.
You can check if your domain is black listed by going to http://mxtoolbox.com and entering your domain name, when the screen returns with a result, then click on the black list check link. If it isn’t black listed it will all come back as green.
There is another kind of block called Grey Listing. This is where the mail looks suspicious, or is thought to be spam, or from a source that does not have a good reputation. These mails are not blocked, but delayed by the receiving system. So they retry. This seems to be what has been happening at Talk Talk on and off.
You can also check Talk Talk’s status by going to here: talktalk email status page.