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).?

[amahle-TT]

Okay, we will look into this for you kindly bear with us, thanks

Hi @KeithFrench, could you please provide insights on the matter above? Thank you.
 

[gmlack]

Yes. I can use Webmail.

But that's irrelevant, as I use an email client that handle multiple accounts.

This is about problems with the SMTP service, i.e. the mail transport, not the mail display.

[amahle-TT]

Have you tried accessing you emails using webmail instead of Thunderbird? 

[gmlack]

It's all Linux.

[amahle-TT]

Thank you, I need to know the operating system on your PC?

Is it

Windows or Mac OS ?

[gmlack]

I use Thunderbird on a PC.

But it never contacts TalkTalk directly.

[amahle-TT]

I understand that it is postfix server process, however in order to log onto your email client you would need to be using a device, we need to know what device you use to access your email client?

[gmlack]

It's none of these.

It's a postfix server process.

My email client talks to my postfix server.  That postfix server then talks to TalkTalk.

[amahle-TT]

it can either be a Personal Computer or a 

Laptop

Smartphone

Tablets

Gaming consoles

[gmlack]

Not sure what you mean by "device".

The postfix server is running an on an Intel NUC system running postfix on Kubuntu.

It connects though my Asus router and a Draytek modem.

[amahle-TT]

I do understand that, and I am running checks so we can find the solution. I need to know what device are you using when accessing your email?

[gmlack]

Accessing email is OK.

It's just sending that is the issue.

I route all of my outgoing email through a postfix server, which is what connects to TalkTalk.

[amahle-TT]

Thank you, what device are you using when accessing your email?

[gmlack]

Yes, I do.

It's current state is:

Uptime 2d 17h 48m 22s.
Last reset after 1d 09h 24m 01s.

Actual speed:

Download: 77155000
Upload: 19999000

Attainable speed:

Download: 98151000
Upload: 22888000

External addr: 89.x.x.x

[amahle-TT]

I am about to run checks, and I need you to confirm if you have a stable internet connection before we start.

[gmlack]

Not sure what you mean by "TalkTalk Internet access", as I wouldn’t be seeing this and replying to it if I didn't have "TalkTalk Internet access".  Receiving email is OK.

I've just sent an email to 3 recipients. This reported:

5.7.8 Error: authentication failed: (reason unavailable)

for all 3 addresses, but them when I forced postfix to resend it a minute later all was OK.

The original message I sent to the 7 recipients is still stuck and fails on every resend attempt. Either for:

5.7.8 Error: authentication failed: (reason unavailable)

or

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

All of this only started to happen at the start of this week.

[amahle-TT]

Can you check your TalkTalk Internet access for me now and let me know if it works? You can do this by trying to reload the site or application you were experiencing problems with, or trying to search for something on the Internet.

[gmlack]

Yes. It's still happening.

I'm also seeing frequent:

5.7.8 Error: authentication failed: (reason unavailable)

messages when connecting to the SMTP server.  (It's a temporary state - the authentication succeeds later without me doing anything).

This also only started this week.

[amahle-TT]

Hi there, please confirm if you are still experiencing the issue so we can proceed thanks. 

[gmlack]

Can no-one shed any light in why the TalkTalk SMTP server is responding:

(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's nothing at my end.  I've been sending a similar message to the same 7 recipients every week for a few years with no problem until now.