Thread: 550 Invalid recipient

Originally Posted by Woodwould

In the past few days I've had a number of emails returned '550 Invalid recipient... User unknown' even though I've simply hit 'reply' to respond to an original email. I've spoken to several of the email senders on the phone and they tell me they are merrily sending and receiving emails on the same accounts to and from other people without issue.

What causes this and is there a fix?

"either you are sending mail via the wrong SMTP server - ie: trying to send via bigpond when connected to optus (for instance) or bigpond has an invalid entry in their mailserver configuration. Under linux this will be relay-domains, mailertable, virtusertable (sendmail), rcpthosts (qmail). No idea what bigpond uses for their mailserver - but good luck getting this fixed, I doubt the Help Desk staff will have a clue on this one."

Plucked off the web for you.

Oo-er! Thanks!

We had a spate of them as well Wood, then it corrected itself again. Are you with iinet?

Thanks.

Hi All

If this has occured recently and then self corrected, it is possibly to do with an upcoming change to the way that the DNS (Domain Name System) works. The DNS takes an easy to remember name of an internet connected machine (eg mail.bigpond.com) and turn it into a hard-for-us-humans-to-remember internet address (eg 61.9.168.249) that computers need in order to actually send stuff on the Internet.

Changes are being made to the top level DNS server systems that add additional data in the responses to queries, to assist in security of the system. Some ISP/other businesses were not ready for this change, and so their servers could not translate the names to numbers, and thus your emails would fail. Changeover to upgraded systems has been causing intermittent problems with some ISPs

It is also possible that the mail server system you are using to send through (the SMTP server in your mail setup) is caching invalid mail server addresses for the recipient organisation whose address is failing. Try sending using Gmail or some other web based mail system.

Brilliant! Thanks. Some of my customers' emails were returning and it was becoming embarrassing (I had to phone a few and explain I wasn't ignoring their emails). So far, I've only noticed the issue with BigPond accounts (I'm with Optusnet).

BTW - a raft of top level DNS servers were changed on 14th April - does this coincide with the problems? The final changes will be completed on 5th May, and at this point there may be some significant issues poorly prepared ISPs & businesses.

Originally Posted by RossM

BTW - a raft of top level DNS servers were changed on 14th April - does this coincide with the problems? The final changes will be completed on 5th May, and at this point there may be some significant issues poorly prepared ISPs & businesses.

I haven't noticed the problem as early as 14th April; just since last Thursday. However, it may be that I haven't had many dealings with Bigpond users.

This problem can be as simple as the recipient having a full e-mail box - it depends on the server being used.

soth

The problem is unlikely to do with any top level DNS changes.

The '550 Invalid Recipient' error is reported by the ISP or recipients mail server and means 'the mail got to the right server(s) but we don't have a user of that name'.
A DNS related problem would be more likely to be a 'HOST NOT FOUND' meaning 'we can't find the mail server that can handle this mail address'.

It's more likely to be an ISP problem where mail servers are being re arranged. As it's Bigpond, this wouldn't surprise me.

It's possible a spammer has sent off spam using your email address as the return address. If the destination address is invalid then it gets bounced back to your address.