URGENT: emails being rejected

[Alex Tweedly]

On 22/03/2016 17:14, Mark Wieder wrote:
>
> A couple of things:
>
> 1. If you're using the on-rev smtp server to send emails, STOP THAT 
> right now. Configure your email client to send email using the smtp 
> server of your isp. You don't need to change the pop server, just the 
> outgoing one.
>
> 2. See point #1.
>
Mark,

why? what's wrong with sending email from on-rev (or any other hosting 
provider) ?

Intuitively, that seems like the right way to do it - my email claims to 
come from "alex at tweedly.net" - surely it's a good thing that it 
originates on the machine that DNS resolves for 'tweedly.net'.  In fact, 
if I send that email instead from my DSL provider then doesn't it become 
indistinguishable from any spammer's email which has my email address in 
the 'from' line, but comes from a machine with no connection to 
'tweedly.net' ?

And, practically, how do I do that ?  Most days I use 3 different ISPs 
(home, office, neighbour's) - would I need to reconfig my email client 
each time ?

(or, to put it another way - what am I missing ? :-)

Thanks
Alex.