> On Jan 16, 2019, at 3:24 PM, Stefan Bauer <cubew...@googlemail.com> wrote:
>
> "Some sites may blacklist you when you are probing them too often (a probe is
> an SMTP session that does not deliver mail), or when you are probing them too
> often for a non-existent address. This is one reason why you should use
> sender address verification sparingly, if at all, when your site receives
> lots of email."
>
> http://www.postfix.org/ADDRESS_VERIFICATION_README.html#limitations
>
> As our user may do mailings from time to time, i do not want to get bad
> reputation by probing microsoft,yahoo whatever too often. :) for remote site,
> i see no difference between sender and recipient verification. in both cases,
> im doing a 'half delivery' of a mail.
But there is a big difference. With sender verification complete
strangers can get your MTA to probe address validity at sites you
never send email to.
With recipient verification, you're at most doubling the number of
RCPT TO commands sent to a site, because you'd otherwise just send
the message, perhaps repeatedly, if it enters your queue and then
soft-fails on each delivery attempt before ultimately bouncing.
If you have bulk senders, you could opt them out of recipient
verification, and perhaps also TLS enforcement.
--
Viktor.
