Hi, 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: relayhost = [smtp-relay.gmail.com]:465 smtp_use_tls = no smtp_sasl_auth_enable = yes smtp_sasl_security_options = noanonymous smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt smtp_tls_wrappermode = yes smtp_tls_security_level = encrypt smtp_connection_cache_destinations = smtp-relay.gmail.com connection_cache_ttl_limit = 5m smtp_destination_concurrency_limit = 1 smtp_destination_rate_delay = 5s And testing with 1000 emails in queue I got: Jan 31 04:51:03 edited--email-relay-2 postfix/smtp[9728]: C0C926255F: to=<carlos.hida...@edited.com>, relay=smtp-relay.gmail.com[74.125.28.28]:465, delay=3541, delays=1885/1656/0.49/0.27, dsn=2.0.0, status=sent (250 2.0.0 OK 1517374263 u74sm4385834itb.2 - gsmtp) I see no conn_use on the log and I'm not sure if cache is also not supported on this SMTPS mode? Thanks for any advice on how to cache the connections!
