Cannot send email to certain email addresses

[#1]

Hello, Hopefully a plusnet techy can pick this up.

I am writing on behalf of my mother.

She has had a Plusnet email address for years and all of a sudden she cannot send me or my brother emails. They get rejected with domain not found. This is definitely not the case and I can prove that these accounts are working perfectly, they are running on office 365 and used all day every day without any errors.

It is also not to do with POP or IMAP settings as she gets the same issue when trying to send via plusnet webmail.

Also when i try to send her an email I also get a rejection from my Office 365 stating that her domain does not exist.

We can send emails both ways to and from my work email, which is on prem exchange behind mimecast security.

She can send emails to Hotmail and Gmail accounts no problem. It seems to be just a handful of domain names.

If any techy can look into this I would really appreciate it, her account is dinahdee and the emails addresses she cannot send to are to the following domains: alexns.com and newtonsmith.co.uk

Thanks in advance

Alex

[#2]

This is the error message that gets returned when i try to send to her:

Error Details

Reported error: 550 5.4.355 Remote server returned recipient domain does not exist -> 550 #5.1.8 Domain of sender address <********@alexns.com> does not exist DSN generated by: PR3PR02MB6490.eurprd02.prod.outlook.com Remote server: avasin04.plus.net

[#3]

Well very strange goings on, someone has done something this morning between 9:10 and 9:40 am because I tested it at 9:10 and it was failing. and now it all works fine.

I wonder how long it will last ?

[#4 · Accepted solution]

Hi @ALEXNS 

A warm welcome to the forums.

You are quite correct - this looked very similar to issues we've seen before, so I escalated this yesterday to one of the SU contacts.  It turned out that this was not the same as pervious incidents.  Apparently the IP address of the name server for the domains in question has acquired a bad reputation in email protection systems.  The IP address has been whitelisted, so this fix should remain fixed!

[#5]

Thats excellent, Thanks very much for escalating it.

My mother has 1 less thing to stress about now.

Hope fully it helpded other people out too, as i am sure those domain cannot be the only ones with that issue.

Cheers and have a good weekend!

[#6]

Hello,

Sadly this has started to happen again now.

Could you please raise the issue again. It is currently happening to alexns.com and newtonsmith.co.uk domains.

Hope you can help again.

Thanks

Alex

[#7]

Hi Alex,

These domains have a common factor - they are both hosted by flex-tek.co.uk - even though their email hosts are different.

Last time this happened, it was down to flex-tek.co.uk's name server having being black-listed...

"The IP for the nameservers had made it onto a list intended to protect mail and other platforms from malicious intent"

The IP address was this was permitted by manual white-listing.  I have asked if that patch has come unstuck ... or is there a new problem with this hosting provider.