Show HN: Listmonk – Fast self-hosted newsletter and mailing list manager

Author here. To give some context on why listmonk was built, at work (regulated financial business), we have to deliver e-mails, mostly important updates, to 1.5mn+ customers regularly. We used phpList for the longest time and then tried MailTrain and Sendy before finally deciding to reinvent the wheel after running into a number of issues, of which, a few important ones are mentioned below.

- Performance. Unreasonably long amounts of time to send out e-mails. phpList degraded to the point of taking several days to process a campaign. listmonk can spawn N goroutines (~threads) and push e-mails to multiple SMTP servers. On a commodity ec2 instance, we're able to send 1.5mn+ e-mails in a couple hours.

- Subscriber imports were extremely slow. Direct integration to keep subscribers in sync with external CRMs was cumbersome. Direct DB inserts were complicated due to the complex table structures. listmonk imports 10k records/sec into a Postgres DB on a commidty ec2 instance.

- Segmentation. Often, we have to rapidly segment users by custom attributes and conditions and relay an update to them. listmonk supports SQL expressions to segment users on their attributes that are defined as arbitrary JSON maps (thanks to Postgres JSONB type).

- Unavailability of dynamic templates. listmonk templates support Go template expressions so it's possible to write logic in messages to make them dynamic.

I would like to add that listmonk is still work in progress and requires a number of essential features before it can come out of alpha.

Looks great! Do you have any plans to support third-party sending APIs (e.g. SES)? I see the reference to SMTP.

I've been looking for a good solution for ad-hoc email campaigns (w/ templates) and for sending "systems" emails to an audience of customers.

I currently look after lists on both MailChimp and EmailOctopus and get frustrated by the flat pricing for the size of the list and not how you engage with the list (e.g. I'd love to see: store your list for $X/mo, or pay $X + (list size * $Y) in the months when you email the list).

The other comments here don't quite tell the whole story; "I never had any problems" is anecdotal - there are plenty of legitimate senders who do run into deliverability issues.

Using an ESP will generally simplify the amount of work necessary to achieve good delivery, but due to the complexities of domain reputation and fingerprinting, very occasionally they can also be the cause of delivery problems.

General guidelines:

- It's a bit harder to predict how deliverability will turn out at smaller ESPs, vs. well-established ones like Sendgrid, SES, Mailgun, and perhaps Mailchimp.

- DKIM, SPF, DMARC (p=none is fine to start; gmail has a guide for deploying dmarc https://support.google.com/a/answer/2466563)

- Use the same root domain everywhere within your email: From, Return-Path, DKIM signature headers; URLs for links and images in the message body. (Separate subdomains are fine, e.g., img.example.com, bounce.example.com)

- Having your sending domain show up in third party email can cause problems. Try to avoid it if possible; use a separate domain as a last resort.

- Send consistently. Some variation in sending patterns will be tolerated, but you'll probably have trouble if you send 500 messages a day most of the time, then once a month you send 100,000 messages.

- Consider a dedicated IP if you're sending over 50,000-ish messages a month.

- You may want to split up transactional email from marketing, sending these from separate IPs and/or subdomains.

- Finally, make sure you're sending email your recipients find valuable and are interested in receiving. Too much disinterest/disengagement can cause delivery issues.

That's what I'm trying to understand, it was an honest question.

So, who does need to be provided with a copy? Just the 'administrators', the people using it to send email?

What about if I modify it and repackage it as monklist or whatever, and charge people to use it. I must give them the source code for listmonk too, and, since another requirement is same licence, the source for my modified version? i.e. monklist couldn't be closed source, but myapp that happens to use listmonk unmodified for sending emails can be?