[MlMt] Return-Path when sending message using an alias

[Glenn Parker]

On 30 Mar 2021, at 8:49, Bill Cole wrote:

> On 30 Mar 2021, at 8:13, Glenn Parker wrote:
>
>> I think the answer is yes, but MailMate can't ask Gmail to do it on 
>> MailMate's behalf. MailMate needs to do what Gmail does, which is to 
>> contact the "alternate" SMTP servers directly to transmit the mail 
>> from a different account. You will need to configure MailMate to have 
>> a full account for each sender address.
>
> There is also a possibility that this is a domain-level problem with 
> an anti-spoofing tactic called 'SPF'. SPF is an acronym for 'Sender 
> Permitted From' and is a means for domain owners to publish via DNS 
> which IP addresses they know to be legitimate sources of mail with 
> envelope senders in their domains (the "MAIL FROM" address, which gets 
> put in the "Return-Path" header at final delivery.) GMail may be set 
> up to override their internal acceptance of a sender in a domain they 
> don't control that has a SPF record forbidding them from sending such 
> email. This makes sense for them to do because there is a strong 
> likelihood that any mail they send which conflicts with SPF will end 
> up being rejected, delivered to a 'spam' folder, or simply dropped.
>
> I apologize for the readability of that paragraph... Put more simply: 
> Even if GMail has verified an alternative sender to their own 
> satisfaction, it is possible that they are enforcing the policy of a 
> domain owner which would otherwise interfere with your deliverability.

Yes, it’s a bit opaque, but I suspect that is the underlying technical 
restriction. It still comes back to the point that MailMate has to do 
the sending directly, rather than delegating the task to Gmail.

For those not familiar with the hidden plumbing of email, sending and 
receiving messages are almost totally separate functions. We tend to 
unify them into a convenient mental model of an email “account”, but 
it’s really two very separate pipes. Having one function working 
successfully does not guarantee that the other will “just work”, 
just like having a sink’s faucet deliver water doesn’t mean that the 
sink’s drain will automatically take it away.

I won’t even try to extend the analogy to what all Gmail is doing, 
because the plumbing would get pretty ugly. The solution is to keep it 
simple, meaning keep all the control inside one application, MailMate, 
instead of trying to piggyback MailMate on Gmail.

Glenn P. Parker
glenn.parker at comcast.net
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