There is no big difference between mass emailing and spamming. If you just sending large amount of emails and breaking the policy of recipient domain it will just treat you as a spammer. There two main thing to consider before starting mass mailing with POSTFIX ..
Maintain your reputation: When sending large amount of emails always maintain your reputation. What is this – Reputation ???
Reputation means just how others see your IP address as a mailer. It’s take slightly a long time to maintain a good reputation in emailing world. Many factors are there like delivery rate, performance, how many resources you are using, working on Opt-IN or non- Opt-IN email list. Until you get a good reputation in email world consider to limit your email rates and delay.
Check providers rate limit: Every email provider has a rate limit. If you cross that limit you will be blocked and get 421 Error: Temporary suspended for emailing.
To resolve this many users use IP rotation to avoid this. But it will be a good practice if you use limit in your postfix configuration.
Let’s configure postfix for outgoing email handling..
smtp_destination_concurrency_limit = 2 smtp_destination_rate_delay = 1s smtp_extra_recipient_limit = 10
smtp_destination_concurrency_limit : Only 2 concurrent connection per domain.
default_destination_rate_delay: Add a delay of 1 second to same receiving domain.
default_extra_recipient_limit: Number of recipient in a single message per domain.
Let’s summarize this, you can send per second 2 email if domain are different. If it’s the same domain you can send single email per second. If your email has more then 10 recipient of the same domain mail will be break in every 10 recipient means email regenerate according to next 10 recipient.
Reload your postfix configuration to make changes, and it’s done.