Recipient Undeliverable (TT512)

[Kilonova]

Today the Lineone email server has bounced/blocked email from a hotmail email address (coming from my sister).  This seems to happen sporadically for no reason.  I receive emails every week from this email address, but today it was blocked.  I expect tomorrow the problem will have gone.  Why does this happen?  It just means my lineone.net email address is not reliable, which is frustrating.

Here's an extract from the error message that the sender received.  Thanks for any guidance you can provide me to resolve this.

kilonova

cm8gb1 rejected your message to the following email addresses:

Username (name@lineone.net) 
The address you sent your message to wasn't found at the destination domain. It might be misspelled or it might not exist. Try to fix the problem by doing one or more of the following:

1. Send the message again, but before you do, delete and retype the address. If your email program automatically suggests an address to use, don't select it.
2. Clear the recipient AutoComplete cache in your email program by following the steps in this article: Status code 5.1.1. Then resend the message, but before you do, be sure to delete and retype the address.
3. Contact the recipient by some other means (by phone, for example) to confirm you're using the right address. Ask them if they've set up an email forwarding rule that could be forwarding your message to an incorrect address.

cm8gb1 gave this error:
P4SLrDoNadLqX Recipient Undeliverable (TT512)

[Gondola]

Attachments will cause email delivery to be deferred for scanning.

Given that there's a lot of spam being directed towards TalkTalk Mail from hotmail outgoing servers there's going to be a lot of mail going into the inbound server buffers awaiting scanning.  So, not the best time to send mail from hotmail with attachments. Better to put the MOV file onto a cloud service like Microsoft OneDrive or Dropbox and enable sharing and just send the sharing link by email. Perhaps you would share this advice with your sister?

If you're also getting a lot of spam directed to your email address it's likely to be because your email address was one of millions captured by onliner spambot malware in 2017. I believe the current waves of spam are using email addresses from that particular data breach. You can find out more by entering your email address at https://haveibeenpwned.com which is a trusted website listing known data breaches.

[Kilonova]

Hi Gondola, 

Thank you for your help.  My sister sent me an simple text email yesterday, approx 1 hr after your message to me, and her email came through OK.  So I am not sure of the reason that her other email didn't come through. 

Her earlier email which received the TT512 error message had a 5Mb .MOV fie attachment, but this filesize is not excessive.  My Lineone mailbox could not have been full, as it is emptied several times/day as I still use POP to access it using Outlook on my laptop and the emails are automatically deleted after they downloaded. 

So, based on your message, I assume the cause was either (a) The Lineone mailbox server was not available for the deliverability check or (b) There was a network block on the hotmail server.   In either case, it seems to be working again now. 

But it does cause me concern that this problem occurs sporadically, and not just with emails from my sister.

Thanks again for your help

kilonova

[Gondola]

Hi @Kilonova 

I've removed your email address from the post that wasn't on display but was hidden under the mailto link. So, having checked that address I can see that it is currently deliverable. 

TT512 is an error code that indicates there was a deliverability issue. The mailbox server may not have been available for the deliverability check or the mailbox may have been flagged as full.  There have also been recent network blocks on hotmail servers due to a huge increase in spam arriving from some hotmail addresses that share the same outgoing server as many other genuine hotmail users such as your sister.  

There seems to be no issue right now so perhaps your sister could try again.

Let us know the result.