Email outgoing problem

[#1]

Hello support team,

I’ve been a long-time user of my PlusNet email address and recently encountered an issue when sending emails to recipients using Outlook (e.g., Outlook.com, Microsoft 365). Since 18th June, messages have been returned with the following error:

550 5.7.515 Access denied, bad outbound sender

The problem persists even when sending via Thunderbird using the following outgoing server settings:

SMTP Server: smtprelay.plus.net
Port: 25

From what I’ve gathered, this Outlook-side rejection is likely due to failing SPF, DKIM, or DMARC authentication checks. Could you please confirm whether PlusNet’s mail servers are correctly configured to pass Microsoft’s sender authentication requirements? And if there are any updates needed to DNS records or outbound mail policies, I’d appreciate your guidance or escalation to Microsoft if needed.

Many thanks, Adjer]

[#2]

@Adjer the problem is being discussed here https://community.plus.net/t5/Email/From-address-doesn-t-meet-the-authentication-requirements/m-p/20...

[#3]

That said ...

---

@Adjer wrote:

The problem persists even when sending via Thunderbird using the following outgoing server settings:

SMTP Server: smtprelay.plus.net
Port: 25

From what I’ve gathered, this Outlook-side rejection is likely due to failing SPF, DKIM, or DMARC authentication checks. Could you please confirm whether PlusNet’s mail servers are correctly configured to pass Microsoft’s sender authentication requirements? And if there are any updates needed to DNS records or outbound mail policies, I’d appreciate your guidance or escalation to Microsoft if needed.

---

Is the wrong configuration...

SMTP Server: relay.plus.net
Port: 587
Encryption:  STARTTLS

As is being discussed elsewhere, the requirement for SPF and DKIM and DMARC and treating *.plus.com as a single bulk senders domain (as in plus.com) is massive over kill.  Microsoft have got this wrong, but they are not likely to yield to common-sense anytime soon.

[#4]

The problem lies with Plusnet - MS have made outlook, msn, etc, stricter and they require a DMARK entry which Plusnet has not provided. Very inconvenient - my workaround is to use Yahoo as the SMTP provider.
If you go to https://www.learndmarc.com/ it will provide full diagnostics, and here is the summary:

--- SPF ---
Domain: riggshome.plus.com
Identity: RFC5321.MailFrom
Auth Result: none
DMARC Alignment: n/a

--- DKIM ---
Domain: plus.com
Selector: 042019
Algorithm: rsa-sha256 (2048-bit)
Auth Result: PASS
DMARC Alignment: PASS

--- DMARC ---
Warning: No DMARC record found – this can severely impact your email deliverability and harm your domain’s reputation!

RFC5322.From domain: riggshome.plus.com
Policy (p=): reject (simulated)
SPF: FAIL
DKIM: PASS
DMARC Result: PASS

--- Final verdict ---
DMARC does not take any specific action regarding message delivery. Generally, this means that the message will be successfully delivered. However, it's important to note that other factors like spam filters can still reject or quarantine a message.

---------------------
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This free service is brought to you by URIports.com - DMARC Monitoring Reinvented.

[#5]

Microsoft's error is to treat *.plus.com as a single bulk sender - not individual senders.

DKIM or SPF alone is adequate.

Where SPF is implemented, DMARC is superfluous as the ?all at the end of the SPF record directs what should be done where that check fails (Hard or Soft fail).

As ever the world is faced with cleaning up the issues created by the big bully boys ... first Gmail, now Microsoft ... their real objective being to drive email users away from the present supplier on to their own platforms.  Microsoft has even had the audacity to blackball the shared use AWS platform - no one using that platform can email a Microsoft account, even with DKIM and SPF configured.

[#6]

Is it likely that this problem will be resolved soon? I'm a Parish Councillor and my Parish Clerk is on an Outlook email address that will no longer accept my Plusnet emails.