Getting "535 ...authentication rejected as source IP has a poor reputation" - and cannot send emails

[#1]

Hi. I am having outgoing email problems. I have been sending/receiving a lot of test emails recently and incoming mail is fine - suggesting my username/mailbox/passwords are all OK.

However, your outgoing SMTP relay.plus.net email server now tells me everytime:

"535 ...authentication rejected as source IP has a poor reputation"

and I cannot send any emails at all now from any email client apps.  I have tried several different email client apps, on different PCs - all similarly bocked.

I have full client/server transcripts available if this helps - from where I got the error message in this thread title.

BTW: outgoing emails using webmail work, which again confirms I have the correct username/mailbox/passwords.

Is there some sort of SMTP email server reset you can do please on my account? to unblock this position whereby your SMTP server regards my "IP address as having poor reputation" ?!  Thanks in advance!

[#2]

Are you sending from a PlusNet broadband connection ?

[#3]

Thanks for your reply.

No, I am no longer a Plusnet broadband customer, as ADSL (all that is available here) is <1 Mbps.

So I use Three 4G mobile broadband now, and have been doing so, successfully, sending/receiving Plusnet email, for over two years now - until yesterday.

( I no longer use Plusnet broadband, but I have retained a Plusnet email-only account, in the hope that fibre will be laid here one day, and I can return to Plusnet broadband! )

NB: Webmail works, sending and receiving emails, for me.

[#4]

I thought that was possibly the case. The problem is that the public IP address you have been allocated by the mobile provider has been marked as the probable source of spam. The Cloudmark anti spam system used by plusnet is therefore refusing to accept mail sent from that ip.

I've seen similar problems occasionally when I've used mobile broadband when on holiday. The marking is usually temporary and the problem goes away in a day or two. However I'm not sure whether Three still use CGNAT , if so then effectively the same public Ip is assigned to lots of connections. In which case the problem will persist. You could try disconnecting your 4g connection and see if you get a different ip when you reconnect.

Webmail will always work because it is hosted on a plusnet server and so when sending mail , you are sending from a plusnet ip and that will always work

[#5]

OK, thanks, makes sense.

Any idea why Plusnet would have accepted Three's IP address for two years+ (since I changed), but no longer?

Any chance of changing Plusnet policy in this regard? (Mad, I know...)

I'll give it a day or two, and also try dis-/re-connecting, to get a different IP address.

[#6]

It could well be that the 'Three' IP you have recently connected to has a 'bad reputation' as noted by @MisterW  above - I suspect, but don't know, that this can change.

It is not 'Plusnet Policy' - it depends on the Cloudmark reputation of that specific IP and the is no way to influence that.

Your best bet is to as you say, give it a couple of days to see if the 'reputation' is repaired, and if not, to try obtaining another IP.

[#7]

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@jab1 wrote:

It is not 'Plusnet Policy' - it depends on the Cloudmark reputation of that specific IP and the is no way to influence that.

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@jab1 , I think you are wrong here - it is Plusnet's policy to block authenticated users from connecting to their SMTP server based on Cloudmark's reputation rating. Lots of MTAs will refuse to pass on mail from disreputable sources, but when you have an authenticated user I believe the SMTP server should accept mail.

Many addresses will have bad reputations, but when they are public shared addresses blocking them for users that you authenticate just makes the e-mail service not fit for purpose.

Personally I wouldn't entrust anything as important as my e-mail to a company that arbitrarily blocks me from sending e-mail, based only on some random address that I have no control over that my device may be connected through.

For the OP, one workaround is to use a VPN to get a "better" address - but there are no guarantees that Cloudmark will like it.

[#8 · Accepted solution]

I concur with the analyses above. I am, of course an "authenticated Plusnet user" and as such should not be blocked. Even Plusnet would agree that, unless they fear my account has been compromised - which is reasonable.  However, that should be dealt with differently - which I think it is - you have to forcibly change your email password TO SOMETHING DIFFERENT (i.e. not just reset it to the same password) - but Plusnet don't advertise this solution much either.

It is indeed galling that Plusnet's email service can be arbitrarily blocked due to something totally outside users' control - leaving the service unworkable - i.e. I cannot send emails!

Anyway: I have found a solution: I have a "spare" 4G SIM, using Superdrug, not Three, which, when used for my broadband connection, naturally gives me a different public IP address.  (Superdrug actually piggy-backs off Three anyway, but my new IP address is sufficiently different.) Now the SMTP server doesn't throw me out.

However, I am now fearful of how long it will be until Plusnet chooses to blacklist this IP range and I have to look yet again at a workaround.

I guess using a VPN permanently may have yielded the same result.

Thanks for posters' help here - especially MisterW for initially pointing me in the right direction.

Please Plusnet - if you're reading this - can you raise this as a Plusnet email policy issue, at the internal tech review meetings you must hold?! It must affect an increasing number of users who use Three Mobile for their broadband.

[#9]

@mooblie , @corringham If you read @MisterW 's post, it clearly points to the originating IP - not the users status, as being the problem, and as such, is outside  direct PN control - they are not responsible for Cloudmarks assessment of that originating IP

[#10]

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@jab1 wrote:

@mooblie , @corringham If you read @MisterW 's post, it clearly points to the originating IP - not the users status, as being the problem, and as such, is outside  direct PN control - they are not responsible for Cloudmarks assessment of that originating IP

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But Plusnet are responsible for using Cloudmarks's assessment in order to block a user from sending e-mail - even though Plusnet themselves can and do authenticate that user.

[#11]

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@mooblie wrote:

It must affect an increasing number of users who use Three Mobile for their broadband.

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It isn't just Three - the same issue has arisen previously with other providers. Plusnet's policy basically means that if you are travelling and using public WiFi the same issue can occur. I'm not aware of any other ISP that blocks authenticated users in this way.

BTW if you are keeping your Plusnet e-mail in case you get FTTP and can return to Plusnet, then it may be a waste of time as Plusnet don't offer FTTP. Personally I'd move my e-mail to somewhere more robust, and have a free choice of ISP.

[#12]

@corringham I agree, but as PN (or most ISPs, I imagine) use a third-party reputation filter, they cannot influence that party's assessment of another providers IP, which is what is being used here as the originating one.

[#13]

I agree that Plusnet can't influence Cloudmark's ranking, but they do have the choice over how they use that information. And they choose to use it incorrectly!

[#14]

@corringham "BTW if you are keeping your Plusnet e-mail in case you get FTTP and can return to Plusnet, then it may be a waste of time as Plusnet don't offer FTTP."

Plusnet don't offer FTTP???!!!  Wow!  If so, I do need to "consider my options", as they say!

[#15]

Is FTTP available in your area?