Hi Rob, 
You mentioned “we tried a direct, person-to-person email, and this also failed.”
Did you send this email using Apple Mail, if so did you receive any error 
message as to ‘why your message could not be delivered to his address?’
Or look in you sent mailbox. Locate the sent message - Go to View > Message > 
All Headers. It perhaps could give you some hint.

You might find some help through Mailman Users group.
https://www.mail-archive.com/mailman-users@python.org/

https://mail.python.org/pipermail/mailman-users/2017-July/082315.html

Cheers,
Ronni

 Ronni Brown’s iPad Pro 12.9-inch 256GB 


> On 2 Mar 2018, at 9:02 am, Tim Law <t...@peoplehelp.com.au> wrote:
> 
> Has he sent an email to your gmail account so that you are sure you have his 
> right email address. I realise you’ve had success using a different send 
> account, but not knowing all the details, I’m just wondering
> 
> Can you get someone else you know with a gmail account to send him a message
> 
> Sent from Tim's iPhone
> 
>> On 2 Mar 2018, at 8:55 am, Rob Phillips <r.phill...@iinet.net.au> wrote:
>> 
>> Initially, they were group emails sent through Mailman (and I checked the 
>> settings). Once it was clear that this failed, we tried a direct, 
>> person-to-person email, and this also failed.
>> 
>> I don't think I've BCCed him at all.
>> 
>> Thinking about it, the person with the admin rights to the Mailman account 
>> is no longer with the organisation, so I haven't seen any bounce messages 
>> from Mailman. These might give a clue as to the problem.
>> 
>> Any bright ideas?
>> Rob
>> 
>>> On 2/3/18 5:45 am, Ronda Brown wrote:
>>> Hi Rob,
>>> 
>>> Are these group emails... bcc‘d? Or emails sent to only one recipient?
>>> 
>>>  Ronni Brown’s iPad Pro 12.9-inch 256GB
>>> 
>>> 
>>>> On 1 Mar 2018, at 10:25 pm, Rob Phillips <r.phill...@iinet.net.au> wrote:
>>>> 
>>>> Greetings
>>>> 
>>>> This is a quite obscure problem, and not directly related to Macs. I'll 
>>>> understand if there is no response... :-)
>>>> 
>>>> I have a gmail email account, which works fine (for most people). There is 
>>>> one person (a Windows user) who never receives my Gmail emails. Everybody 
>>>> else does!
>>>> 
>>>> I have told him repeatedly that the problem must be at his end. He has 
>>>> made sure that this email address isn't in his junk or blocked list.
>>>> 
>>>> He says that he has reviewed all the email security settings on his 
>>>> computer.
>>>> 
>>>>> Re emails - your iinet ones are getting through to me; it's the gmails 
>>>>> that don't even though it's on my safer senders list and not on the 
>>>>> blocked one. Can't seem to get around this one but have changed the last 
>>>>> possible security setting.
>>>> I'm just wondering if there's some setting on Gmail which might restrict 
>>>> my messages going to him.
>>>> 
>>>> If nobody knows, which is a good forum to ask?
>>>> 
>>>> Cheers
>>>> 
>>>> Rob
>>>> 
>>> -- 
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