A warm welcome to all of the new members posting here.
References to "domain does not exist" is a distinct problem which is being worked on.
The general forwarding reports somewhat sound like SPF compliance failures - in which case Reg123's advice to ask Plusnet to turn it off is fundamentally wrong.
https://en.wikipedia.org/wiki/Sender_Policy_Framework
Sender Policy Framework (SPF) is an email authentication method designed to detect forged sender addresses in emails (email spoofing), a technique often used in phishing and email spam.
SPF allows the receiver to check that an email claiming to come from a specific domain comes from an IP address authorized by that domain's administrators.
INBOUND SPF verification is a measure to reduce SPAM proliferation, it is facilitated where the SENDER's email address specifies a permitted SMTP sender restriction. For example it might state that for me@mydomain.co.uk ONLY smtp.mydomain.co.uk is a valid email relay service. The receiving email service looks to see if there is a SPF constraint and verifies that the email originated from the specified SMTP, if it does the email is accepted, if it does not it is rejected.
For straight forward from A to C email messaging this largely works without issue. HOWEVER where there is an intermediary A to B to C as in email forwarding, life gets messy.
If A has a SPF restriction B checks that the email from A came from a permitted sender and accepts delivery. Unless the provider of email service B (in this case Reg123) has set things up properly, when the email is subsequently forwarded, it is done so as being from A sent by B's SMTP server. When received at C, the SPF check fails because B is not an acceptable SMTP for A.
If the above is the correct analysis of the issue, then the right solution is for Reg123 to ensure that they have correctly implemented SRS … not for Plusnet to switch off the highly desirable inbound SPF spam prevention measures.
https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme
In a number of cases, including change of email address and mailing lists, an MTA accepts an email message that is not destined to a local mailbox but needs to be forwarded. In such cases, the question arises of who deserves to receive any related bounce message. In general, that is either the author, or a person or other entity who administers the forwarding itself.[2] Sending bounces to the author is administratively simpler and used to be accomplished by just keeping the original envelope sender. However, if the author address is subject to a strict SPF policy (-all) and the target MTA happens to enforce it, the forwarding transaction can be rejected.
Sorry if all of this appears to be very technical … but the space is very technical.
I implore all users experiencing this problem in the first instance to ask Reg123 if when forwarding emails, are they applying SRS on the forwarded emails?
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
