> On Jan 30, 2018, at 11:53 PM, Vladimir Hidalgo <vladimiro...@gmail.com> wrote:
>
> I'm using Postfix inside Google Cloud Compute Engine with outbound
> port 25 blocked by default and I want to use Postfix to relay email
> from my org.
>
> I've setup both SSL and TLS modes successfully (diff installations)
> but the problem is that I generate an unique email for each of the
> 1000 recipients and sending this causes a DoS alert on Gmail after
> about 50 consecutive emails.
>
> Their support advice to reuse the connection to send more than 1 email
> per connection, but as per the documentation TLS / 587 is not
> supported for connection caching.
>
> What about SMTPS on port 465?. I've successfully configured Postfix by using:
Postfix does not support TLS connection re-use. The destination port
plays no role in this, nor does use of wrapper-mode vs. STARTTLS.
I'm afraid you'll need to find a nexthop relay that is willing to accept
your mail traffic one message per connection. You can configure a TLS
session cache (smtp_tls_session_cache_database) to reduce the cost of
setting up TLS for each message. This may not appease the resource
limits imposed by your current relay provider, but it won't hurt.
--
Viktor.
