[GLLUG] OT: GMail handling SPF records of forwarded messages

[gvim]

Can anyone explain GMail's confusing handling of this SPF/forwarding 
scenario?

Email for:

jane at surname.uk.com

... is forwarded via her domain host 123-Reg to:

jane.surname at gmail.com

.... which works fine for several years until she begins work at the NHS 
and finds staff using @nhs.net email addresses cannot get messages 
through to her via jane at surname.uk.com resulting in this bounce:

**************************************************
A message that you sent has not yet been delivered to one or more of its
recipients after more than 6 hours on the queue on smtp02.mailcore.me.

The message identifier is:     1b2glo-0004Lq-JX
The date of the message is:    Tue, 17 May 2016 16:11:40 +0100
The subject of the message is: Test on Tuesday 17 May

The address to which the message has not yet been delivered is:

jane.surname at gmail.com
    (generated from jane at surname.uk.com)
    Delay reason: SMTP error from remote mail server after end of data:
    host alt3.gmail-smtp-in.l.google.com [64.233.189.26]:
    421-4.7.0 [94.136.40.64      15] The SPF record of the sending 
domain has one or
    421-4.7.0 more suspicious entries. To protect our users from spam, 
mail sent
    421-4.7.0 from your IP address has been temporarily rate limited. 
Please visit
    421-4.7.0 
https://support.google.com/mail/answer/81126#authentication for more
    421 4.7.0 information. s69si16983236ita.53 - gsmtp
*******************************************************

94.136.40.64 is the IP of one of 123-Reg's mailservers at mailcore.me 
but the bounce refers to this IP in the context of "the sending domain" 
which would be nhs.net. This is what's confusing me as the NHS admins 
assured Jane that there is nothing wrong with their SPF records.

I setup an SPF record for surname.uk.com at 123-Reg but it hasn't 
altered the problem with @nhs.net emails. A further complication is that 
emails from other origins are getting through to jane at surname.uk.com.

Any ideas?

gvim