TalkTalk SMTP server rejecting some connexions (but not all).

[gmlack]

I send my email via a local SMTP server (mine - Postfix).

This has worked well for several years.

But this morning, when I tried to send an email to 7 recipients, it failed and the log of connexions to TalkTalk shows:

2025-11-03T11:17:52.300609+00:00 benuc postfix/qmgr[1993]: 3699C5F2CB: from=<MyAccount@dsl.pipex.com>, size=3070, nrcpt=7 (queue active)
2025-11-03T11:17:57.392258+00:00 benuc postfix/smtpd[356593]: disconnect from mylaptop.homenet[192.168.1.10] ehlo=2 starttls=1 auth=1 mail=1 rcpt=7 data=1 quit=1 commands=14
2025-11-03T11:17:59.968276+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt1@btinternet.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn
=4.7.1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.970646+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt2@btinternet.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn
=4.7.1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.973066+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt3@gmail.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn=4.7.
1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.976523+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt4@gmail.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn=4.7.
1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.978996+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt5@gmail.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn=4.7.
1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.981324+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt6@hotmail.co.uk>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, dsn=
4.7.1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))
2025-11-03T11:17:59.984062+00:00 benuc postfix/smtp[356597]: 3699C5F2CB: to=<Rcpt7@example.plus.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=7.7, delays=0.09/0.02/0.26/7.3, d
sn=4.7.1, status=SOFTBOUNCE (host smtp.talktalk.net[153.92.174.230] said: 550 5.7.1  Reject for policy reason (in reply to end of DATA command))

It continues to give this response every time the Postfix server tries resending.

It appears that I can send emails to 1 addressee, e.g.:

2025-11-03T16:45:00.112865+00:00 benuc postfix/qmgr[1993]: 1401C5F419: from=<MyAccount@dsl.pipex.com>, size=2041, nrcpt=1 (queue active)
2025-11-03T16:45:01.591676+00:00 benuc postfix/smtp[371777]: 1401C5F419: to=<Rcpt1@icloud.com>, relay=smtp.talktalk.net[153.92.174.230]:587, delay=1.5, delays=0.05/0.01/0.25/1.2, dsn=2.0
.0, status=sent (250 2.0.0 Ok: queued as 64308A40142)
2025-11-03T16:45:01.592070+00:00 benuc postfix/qmgr[1993]: 1401C5F419: removed

so there's nothing wrong with authentication (and, indeed, I'm receiving incoming mail OK).

So, what has changed on the TalkTalk SMTP server (nothing changed at my end).?

[Philile-TT]

Thank you for confirming that, I will take that up with the team. 

[gmlack]

No longer having issues, but unless the cause is investigated it is always likely to happen again.

[Philile-TT]

@gmlack are you still having issues? 

[KeithFrench]

Because I am a Community Star.

[gmlack]

• Being just a customer myself, not a TalkTalk employee, all I can do is to refer this back to them. You will not be able to see my escalation, but I will do it now for you.

How do you escalate something?

And how, as a non-TT employee,  can you do this on behalf of someone else?

Intrigued...

[KeithFrench]

Yes I know they are standard SMTP rejections. Whilst I understand fully the SMTP protocol, I do not profess to be an expert on email servers.

Being just a customer myself, not a TalkTalk employee, all I can do is to refer this back to them. You will not be able to see my escalation, but I will do it now for you.

[gmlack]

No, these are standard SMTP error responses (see RFC2821).

That RFC states:

                                                       If it declines to
   relay mail to a particular address for policy reasons, a 550 response
   SHOULD be returned.

However, for this to have happened to all 7 at the same time implies that it isn't an individual addressee that is being refused, but rather the entire message. A view that is bolstered by the fact that I could send other messages to all 7 whilst this was being rejected.

So it is a TalkTalk issue, and only  they can shed further light on the issue.

But, as I noted above, the message was finally accepted this morning, without me changing anything (just as I had changed northing when it first started).

In the absence of any comment about what actually changed at the TalkTalk end I'll just have to hope it doesn't happen again, but given that some of my accounts get disabled from time to time with no explanation, I'm not hopeful of that.

So I've set up a monitor to email me if mail gets stuck (and that mail delivery is local to me....).

[KeithFrench]

Hi @gmlack 

I think that you would be better off speaking to Postfix's tech support, as these are their error codes.

[KeithFrench]

Well that is the limit of my help.

[gmlack]

Well, at 07:40:52 this morning, after a delay of 332572s (3days 20h 22m 52s) the message was accepted by TalkTalk (having last been rejected at 07:20:46).

Was this related to a change by TalkTalk, or just random events.?

It's arrival caused some confusion, as it started by saying "It's Monday, so...", but my explanation to all 7 concerned has been delivered immediately this time.

[Mandisa-TT]

Thank you for the promptly response, @KeithFrench will look into it for you.

[gmlack]

Rebooting my router gave me a new IP address (rebooting the modem did not, but it is in pass-through mode).

This has made no difference.  I still get the 

550 5.7.1  Reject for policy reason (in reply to end of DATA command)

error. 

[gmlack]

But there is no reason for TalkTalk to not trust its own allocated IP address server which has authenticated with a TalkTalk account.

And there surely can be no reason to not trust it for just one message when it is trusted for other messages.

I think those reasons refer to SMTP servers talking between domains.

[KeithFrench]

The WAN IP address is allocated by TalkTalk to your router; it is dynamic and so changes from time to time. Sometimes these public addresses that are allocated to any ISP customer have a poor reputation & can be blocked by some email systems. A blacklisted WAN IP address is the number one cause. So please can you try & get another one for yyour router, as I outlined in my previous post.

The Google search for your error comes with this as its first match:-

The Postfix error 550 5.7.1 means the receiving email server is rejecting the message because it doesn't trust the sender, often due to security policies, unauthorized access attempts, or a poor sender reputation. Common causes include the sender's IP address being blacklisted, misconfigured server settings like missing authentication, or sending unsolicited bulk email. To fix this, verify email authentication records (SPF, DKIM, DMARC), check your IP address against blacklists, ensure your server isn't configured to send unsolicited mail, and confirm your Postfix relay settings are correct, such as ensuring localhost is properly defined. 

Common causes

• Blacklisted IP: The server you're sending from is on a blacklist, often due to past spam activity.
• Authentication failure: The recipient server cannot verify your domain's legitimacy due to missing or incorrect SPF, DKIM, or DMARC records.
• Unauthorized relay: Your Postfix server is configured to reject mail from an IP address that is not listed in its mynetworks parameter.
• Unsolicited mail: The recipient server has flagged the email as spam, or your server is sending too many emails too quickly.
• Misconfiguration: The email server's settings are incorrect, such as improper client authentication or invalid headers. 
  

[gmlack]

I could, but the WAN address I have is always allocated by TalkTalk, so not sure why a different address would have a different result.

[KeithFrench]

Hi @gmlack 

I have just started to look into this & your logs (to someone who has never used Postix) do not appear to give a reason for the SOFTBOUNCE. However, Googling 550 5.7.1 it looks like your router's WAN IP address is not trusted due to some security policies. Perhaps you could try getting a new WAN IP address by turning your router off for at least 30 minutes. If that does not do it (a lot depends on the type of broadband that you have), you may need to try it turned off overnight.

[gmlack]

Will send later...

[KeithFrench]

The error details would be useful @gmlack . You can always PM them to me to preserve your privacy if you want.

[gmlack]

I can supply postfix debug logs (from my end) if desired.

They show connexion, successful authentication, sending the 7 RCPT commands, then the DATA, and then the close with a 550 error.

[KeithFrench]

Hi @gmlack @amahle-TT 

I'll get back to you both a bit later.