topic Re: Mail delivery failed in Email

Mail delivery failed: blocked using Spamhaus

Boink — Sun, 23 Feb 2025 10:05:00 GMT

Hi, I can't send email to hotmail accounts, getting the following error:

Diagnostic-Code: smtp; 550 5.7.1 Service unavailable, Client host blocked using Spamhaus

Re: Mail delivery failed

Marsh — Mon, 24 Feb 2025 10:00:42 GMT

Hey @Boink,

Could you please let us know if your getting this error on our webmail website or while using a third-party email client for our email service?

Re: Mail delivery failed

Boink — Mon, 24 Feb 2025 10:49:54 GMT

Third party mail client (Thunderbird on Windows PC)

Managed to get my IP unlisted (for now...) by following their link to Spamhouse.

I did not abuse the email system, seems they don't like non-microsoft clients...

Re: Mail delivery failed

Peter123 — Tue, 04 Mar 2025 22:58:44 GMT

I have started to get this error too. Just recently in the last week or so.

Frome the SpamHaus website, I get

Outbound Email policy of Plusnet Plc for this IP range

It is the policy of Plusnet Plc that unauthenticated email sent from this IP address should be sent out only via the designated outbound mail server allocated to Plusnet Plc customers. To find the hostname of the correct mail server to use, customers should consult the original signup documentation or contact Plusnet Plc Technical Support.

I have not changed anything here!! What should I set the "outbound mail server" to be? I'm using Thunderbird on Debian.

Regards,

Peter

Re: Mail delivery failed

Townman — Wed, 05 Mar 2025 00:36:43 GMT

A few questions...

Are you connecting over a Plusnet supplied internet service?
Are you using a VPN service?
Are you sending from you@youraccount.plus.com ?
Are you using relay.plus.net as the SMTP server ?
Is the outbound service configured to require username & password?
What is the A.B.C.x part of your external IP address ?
Who is the recipient domain ?

That BL should only apply where a user is attempting to run their own SMTP service on they home IP address. something is not quite right here, hopefully answers to each of the above questions should help to better profile the issue.

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 11:52:53 GMT

Hi TownMan,

Thanks for looking at this. Re your questions;

1) Yes

2) No

3) Yes

4) My email server settings say 'POP Mail Server' and mail.plus.net

(These have not changed for many years)

5) Yes

6) My IP address is set dynamically each time I start the router.

Right now its 87.114.51.77, yesterday I was using 91.125.55.122 and 146.66.42.104

with the same result. All these IP address are on the SpamHaus Policy Block List (PBL)

7) I am blocked from sending email to fpc-pascal@lists.freepascal.org

I first noticed this problem on 26th Feb. I could post to the mailing OK on 21st Feb

I'm not aware of any issues with other recipients

So what changed between 21st Feb & 26th Feb ?

Regards,

Peter

Re: Mail delivery failed

MisterW — Wed, 05 Mar 2025 12:01:20 GMT

4) My email server settings say 'POP Mail Server' and mail.plus.net

(These have not changed for many years)

@Peter123 those are the incoming server settings, @Townman needs to know if the outgoing server is set to relay.plus.net ?

All these IP address are on the SpamHaus Policy Block List (PBL)

All dynamic IP addresses are on the PBL. It indicates that mail should not be sent directly from those IP addresses. Providing your outgoing server is set to relay.plus.net then it should not be a problem.

I am blocked from sending email to fpc-pascal@lists.freepascal.org

It seems as though that destination mail server is using the PBL incorrectly ( its not unheard of! )

Re: Mail delivery failed

Townman — Wed, 05 Mar 2025 12:17:01 GMT

@Peter123

@MisterW has probably articulated well the issue - bad use of PBL by the receiving domain. If your emails are being delivered successfully elsewhere, then the issue must be within the receiving email service. As noted - it is far from being unknown!

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 12:39:26 GMT

Hi MisterW,

I checked the outgoing server and it is set to relay.plus.net. So while there "should not be a problem",

there is.

The FreePascal folks say the problem is that PlusNet should not be sending their own IP addresses to the PBL.

Regards,

Peter

Re: Mail delivery failed

MisterW — Wed, 05 Mar 2025 13:02:43 GMT

@Peter123

The FreePascal folks say the problem is that PlusNet should not be sending their own IP addresses to the PBL.

I'm sorry but they're wrong!

This https://www.spamhaus.org/blocklists/policy-blocklist/ explains the use of the PBL

The PBL detects end-user IP address ranges which should not be attempting to directly deliver unauthenticated SMTP email to any Internet mail server. All the email originated by an IP listed in PBL is expected to be submitted - using authentication - to a SMTP server which delivers it to destination. The SMTP server can be either supplied by the ISP connecting the IP or by an external mail service.

You are NOT sending email directly from your IP address, it IS going via the ISP ( Plusnet ) mail server. Hence Freepascal should NOT be checking your IP address.

One further question, though ? the above PBL policy does state 'is expected to be submitted - using authentication' but I'm not sure that is a definite requirement.

Is your email client configured to use authentication on the outgoing (SMTP) server ? you should use your PLusnet account name and password.

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 13:04:56 GMT

While I am only seeing isssues with the FPC mailing list, 2 secs on Google searching for SpamHaus and PlusNet

reveals many reports of this issue with PlusNet email, most with no resolution.

However I did find one fix, when a user was blocked from Microsoft 365.

The thread is from 4th Nov 2022. (First page of Google results, per above)

[BobPullen]

I've assigned you a static IP. You'll need to disconnect/reconnect for it to be applied. For verification purposes, it's in the 84.92.0.0/16 range.

[GMC]

Thank you Bob for setting up the static IP. I can confirm that having a static IP has solved the problem although I appreciate that there was something strange going on with the dynamic IP addresses flagging.

Is there any chance I could be assign an (unblocked) static IP address? Based on GMC's experience, that should fix the issue.

Regards,

Peter

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 13:14:11 GMT

Hi MisterW,

My last post crossed with yours. A key peice of missing information here, is who changed what between Feb 21st & Feb 26th? Any ideas? I'm not aware of anything significant at my end.

Re email settings, I'm using Thunderbird, and Security Settings are

[Connection Security] SSL/TLS

[Authentication method] Normal password

Regards,

Peter

Re: Mail delivery failed

Townman — Wed, 05 Mar 2025 13:27:47 GMT

Inbound is TLS/SSL

Outbound is STARTTLS

However, if you have the outbound settings significantly wrong, you'd not be able to send at all.

Static IP address are no longer available and that "resolution" was not a fix, but an avoidance measure. The action by this mail hosting service is totally inappropriate.

Historically static IP addresses DID permit users to run their own email servers, in which case those IP addresses were permitted to send (MX to MX) email messages direct. Such is not permitted on dynamically allocated IP addresses.

The 'rub' here is that you are NOT sending email direct, you are sending it via PlusNet's official relay service and thus there is no applicability of this block policy. This is not the first time we have seem the total misunderstanding of the application of that block list.

The receiving party is wrong here.

Re: Mail delivery failed

MisterW — Wed, 05 Mar 2025 13:28:31 GMT

A key peice of missing information here, is who changed what between Feb 21st & Feb 26th? Any ideas? I'm not aware of anything significant at my end.

@Peter123 it won't be anything at your end and all dynamic IP addresses have ALWAYS been on the PBL. So unless one of the plusnet mail servers has got itself on the PBL (very unlikely and if it has then the networks team will have proactively requested it to be removed!) , the change will be at the receiving end.

Is there any chance I could be assign an (unblocked) static IP address? Based on GMC's experience, that should fix the issue.

Static IPs are not on the PBL (well not if requested to be removed) since its legitimate for static IP users to be running their own mail server. However static IP's are no longer available to customers who don't already have them.

The fact that your email to other destinations works fine does tend to confirm that the problem is at the receiving end.

I have my email with a third-party supplier, if you like, I can PM you an email address to send a test email to. Then I'll check the headers to see if there's anything that might indicate a problem. Let me know if you'd like to try that ?

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 13:31:23 GMT

Outbound was None. I've just changed it STARTTLS, and will check results.

It was probably set to None for at least the last ten years!

Sadly, no change. I'm still blocked!

Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host [84.93.230.227] blocked using sbl-xbl.spamhaus.org;

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 13:33:10 GMT

My outbound settings say

Port: 25 (Default:587)

Should I try changing the port number?

Re: Mail delivery failed

MisterW — Wed, 05 Mar 2025 13:41:29 GMT

Yes, change it to 587. Port 25 is not supposed to be used for submitting email to a mail server, its the port used for communication BETWEEN mail servers.

Client host [84.93.230.227] blocked using sbl-xbl.spamhaus.org;

That IP is actually one of the PN mail servers, so it would seem ITs got itself on a blocklist. Let me just have a look...

Re: Mail delivery failed

Townman — Wed, 05 Mar 2025 13:40:58 GMT

Though it might be seen to work, technically, yes. Port 587 is for message submission from an email client, whilst port 25 is for MX to MX message relay.

Given that you have highlighted this, I'm wondering if there is any indication to the remote end which port number this was submitted on (either directly or indirectly) which leads to the remote end believing that you are acting as a message relaying service (and therefore subject to the block list policy) rather than recognising that you are simply a message submission agent and not subject to the policy.

I await with interest to see if there is anything to this theorem!

Re: Mail delivery failed

Peter123 — Wed, 05 Mar 2025 13:51:53 GMT

Hi guys,

Changing the port made no difference, still blocked. Full rejection message follows;

      This is an automatically generated Delivery Status Notification.      

Delivery to the following recipients failed permanently:

   * fpc-pascal@lists.freepascal.org

Reason: A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server ?? responded with: ** fpc-pascal@lists.freepascal.org ??:?? This message was created automatically by mail delivery software on the server .

Reporting-MTA: dns; avasout-ptp-001 [84.93.230.227]
Received-From-MTA: dns; [192.168.1.10] [87.114.51.77]
Arrival-Date: Wed, 05 Mar 2025 13:45:59 +0000


Final-recipient: rfc822; fpc-pascal@lists.freepascal.org
Diagnostic-Code: smtp; 554 5.7.1 Service unavailable; Client host [84.93.230.227] blocked using sbl-xbl.spamhaus.org; Error: open resolver; https://check.spamhaus.org/returnc/pub/2a01:4f8:0:a231::add:2d/

Last-attempt-Date: Wed, 05 Mar 2025 13:46:01 +0000

Re: Mail delivery failed

MisterW — Wed, 05 Mar 2025 13:52:59 GMT

@Peter123 further to my last post. It looks like one of the mail servers is on the Anonmails DNSBL which is likely what's causing the issue. Its not a PBL problem and I've tagged one of the staff in the Superuser area to check and attempt to get the server removed.