we are running a big party-picture website with more then 250.000 users.
~100.000 of them are signed up to a newsletter we send 3-4times a month (or would like to send!).
Currently we have 1 Webserver (debian, 32gb ram, 8x xeon) with a valid PTR and SPF record, that runs a Cronjob and send the mails with PHP to localhost sendmail.
Unfortunately i see a lot of error messages in the mail.info log.
I think its because sendmail somehow sends too fast to the smtp servers from the users and gets blacklisted for around 24hours.
I am thinking about to set up an exim4 or postfix server to gracefuller handling of those mails. The webserver will send to the local exim or postfix-server, and the local mailserver to the extern servers.
Do you guys have any other solutions?
Maybe some 3rd Party massmail providers or something?
If you are able to, you could code a PHP script that say sends 10 emails then waits 15 seconds and sends the next 10 etc. - this is how WHMCS billing system now works with its mass mail feature and it is very successful.