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550 error on occasion

FIXED
washboardmac
Grafter
Posts: 64
Thanks: 4
Registered: ‎26-03-2013

550 error on occasion

Hi

For a few years I've been happy sending mails from my Synology NAS, which relays via Plusnet.  However in the past couple of weeks I've been getting sent email bounced back with the following error message (addresses changed!)

Reporting-MTA: dns; mydomain.co.uk
X-Postfix-Queue-ID: 48F9D49E
X-Postfix-Sender: rfc822; me@mydomain.co.uk
Arrival-Date: Tue, 7 Nov 2017 23:50:46 +0000 (GMT)

Final-Recipient: rfc822; the.recipient@yahoo.com
Original-Recipient: rfc822;the.recipient@yahoo.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; relay.plus.net
Diagnostic-Code: smtp; 550 <me@mydomain.co.uk> sender rejected - invalid
domain (no MX or A record)

 

This doesn't always happens and if I resend the message it seems to work, though I have had reports of messages not being received.

I know we always claim that nothing has been changed but I'm pretty sure that it hasn't - NAS updates aside.

I've just done a test to/from my gmail account.

mydomain -> gmail - worked

gmail -> mydomain - worked

mydomain -> gmail - failed, resent - worked

gmail > mydomain - worked

mydomain -> gmail - worked

As the error text is related to A/MX records could the problem lie with my domain registrar?

Any ideas welcome.

Cheers

Andy

17 REPLIES
Plusnet Help Team
Plusnet Help Team
Posts: 13,536
Thanks: 251
Fixes: 69
Registered: ‎27-04-2007

Re: 550 error on occasion

Hi there, 


Can you PM me the domain so I can run an NS lookup and have a look at the records set against it?

 

Adam

If this post resolved your issue please click the 'This fixed my problem' button
 Adam Walker
 Plusnet Help Team
washboardmac
Grafter
Posts: 64
Thanks: 4
Registered: ‎26-03-2013

Re: 550 error on occasion

Hi Adam

Pm'd a few days ago.  Any progress on this.  I note another user has reported the same problem:

https://community.plus.net/t5/Email/False-rejection-of-valid-sender-domain/td-p/1492200

Cheers

 

Andy

washboardmac
Grafter
Posts: 64
Thanks: 4
Registered: ‎26-03-2013

Re: 550 error on occasion

Apologies for replying to my own thread...

 

but this situation is still happening.

 

Just today - 27 Nov - I tried to send an email and twice got the same error - this is not an account I use much but the communications are important.  I sent it a third time and that time no error message was generated, though having not heard back I've no confidence that all's well. I note that another poster is having the same issues.

Either this works or it doesn't, either my A/MX records are correct or they aren't.

I did send a PM but have heard nothing back.

Looking forward to an official reply.

Andy

Community Gaffer
Community Gaffer
Posts: 13,479
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Registered: ‎04-04-2007

Re: 550 error on occasion

Hi Andy,

Chuck a PM my way and I'll try to help, just need to know the domain in question.

The error is pretty cut and dry though. For one reason or another our relay server is failing to lookup the MX records for your domain.

Bob Pullen
Plusnet Product Team
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washboardmac
Grafter
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Registered: ‎26-03-2013

Re: 550 error on occasion

Hi Bob

PM sent

Many thanks

Andy

Community Gaffer
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Re: 550 error on occasion

This doesn't look right to me.

An MX lookup on your domain is returning a CNAME record!?

~ $ dig [redacted].co.uk mx @212.159.6.10

; <<>> DiG 9.9.5-9+deb8u13-Raspbian <<>> [redacted].co.uk mx @212.159.6.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16544
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;[redacted].co.uk.           IN      MX

;; ANSWER SECTION:
[redacted].co.uk.    3600    IN      CNAME   [redacted].diskstation.me.

;; AUTHORITY SECTION:
diskstation.me.         300     IN      SOA     ddns-ns1.quickconnect.to. domain.synology.com. 10259881 3600 300 604800 3600

Whilst some servers might handle this, I'm fairly certain it's against RFC's.

As to why the issue is only intermittent when using our relays, I don't know Huh

Bob Pullen
Plusnet Product Team
If I've been helpful then please give thanks ⤵

Community Gaffer
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Re: 550 error on occasion

To clarify how to address this, an MX record should be created in DNS to point to a subdomain. That subdomain should then be pointed to an IP address using an A record.

e.g:

plus.net.              MX         mx.avasin.plus.net.
mx.avasin.plus.net.    A          212.159.9.200

Bob Pullen
Plusnet Product Team
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washboardmac
Grafter
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Registered: ‎26-03-2013

Re: 550 error on occasion

Hi Bob

Thanks for the prompt replies.

I'm a bit out of my technical comfort zone now!!!  It would have been me who set up the original CNAME entries at 1&1.  I wasn't running a mail server originally and the CNAME worked fine for the Synology DDNS service.  When I added the mail server it just worked.  I have to hang my head in shame with regard to not knowing about RFCs.

From your second reply I guess the only proper fix is to have a fixed IP address?

Cheers

Andy

Community Gaffer
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Re: 550 error on occasion

Fix

Try creating an MX record with 1&1 using priority 5 (doesn't really matter what priority you use to be fair) and point it to the DDNS address, i.e. the same destination you've used for the CNAME.

The MX record should take priority, and I'm hoping this will resolve your problem.

Edit: you may need to wait for DNS to propagate, so wait until tomorrow before drawing any conclusions.

Bob Pullen
Plusnet Product Team
If I've been helpful then please give thanks ⤵

washboardmac
Grafter
Posts: 64
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Registered: ‎26-03-2013

Re: 550 error on occasion

Hi again

OK, that sounds like something I can handle.  Odd that it started throwing up errors just recently.

I'll have a look at this tomorrow morning - it's too late now!  I'll let you know.

Many thanks for your expert assistance.

Andy

Community Gaffer
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Registered: ‎04-04-2007

Re: 550 error on occasion

Agree, odd that it's only just started being a problem, however I'm not party to what Synology might have been doing behind the scenes with their DDNS solution.

Let me know how you get on.

Bob Pullen
Plusnet Product Team
If I've been helpful then please give thanks ⤵

washboardmac
Grafter
Posts: 64
Thanks: 4
Registered: ‎26-03-2013

Re: 550 error on occasion

Hi Bob

I set up the MX record as you recommended and finally all seems well but with one caveat.

I had to change my email clients' SMTP and IMAP hosts to my DDNS name rather than my domain name otherwise the servers weren't found.

Again many thanks.

Andy

PS it's due to the level of support found on this forum that I stay with this ISP

Superuser
Superuser
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Registered: ‎06-04-2007

Re: 550 error on occasion

The server host name settings in your email client should be those where the servers reside. Unless you are running your own mail server it would be unusual for these to reflect your domain name.

For example on Plusnet the IMAP host is imap.plus.net and for SMTP it is relay.plus.net.

David
washboardmac
Grafter
Posts: 64
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Registered: ‎26-03-2013

Re: 550 error on occasion

Hi Spraxyt

Thanks for your contributon.

However I am running my own mail server, on my Synology NAS.  Previously I could locate the hosts via the domain name but now have to use the DDNS name.  I did notice when setting up the correct MX record info that my CNAME on the www subdomain had become reset.  Putting this back restored my personal website to normaility.  I suspect that the CNAME on the domain itself has vanished too.

I don't mind as long as it works!

Cheers

Andy