How can I set up a self-hosted email queue system for sending 5 million emails a month?

I once built a similar system using HAProxy in front of several Postfix servers configured for round robin. You can make one Postfix instance handle immediate deliveries while a second one manages the queuing. Make sure to keep track of your volume to avoid hitting limits.

Consider using Postfix for your setup. You can configure smtp_destination_rate_delay and smtp_destination_concurrency_limit to manage your sending pace. Additionally, setting up a queue runner with proper retry rules could help in handling delivery without running into rate limits.

Setting up a self-hosted email system for that volume sounds challenging! Many self-hosted solutions can easily end up on spam blacklists. You might want to explore distributing your email goals across multiple SMTP accounts to reduce the risk of being rate limited and blocked as spam. Just throwing all that volume through one channel is a bit risky.

Honestly, it might just be better to work with a professional email marketing service. Running a self-hosted solution requires constant monitoring, and you might end up needing dedicated personnel just to manage deliverability. These services usually have systems in place to deal with these challenges efficiently.

Just a note, if you're relying heavily on your current SMTP provider, that might be the crux of your bottleneck. Your best bet could be discussing enterprise-level solutions with companies like Brevo or Klaviyo that cater to high-volume senders.