Requirements

Software

Component	Version	Why
PHP	8.4 or later	Laravel 13 and the Symfony Mailer 8 bridges.
PostgreSQL	15 or later	`jsonb`, partial indexes, filtered aggregates. MySQL is not supported.
Redis	7 or later	Queues (Horizon), cache, sessions.
Node.js	22 or later	Building the interface, and rendering MJML at send time.
Composer	2	PHP dependencies.
Nginx or Apache		The web server in front of PHP-FPM.

PHP extensions: pdo_pgsql, redis, intl, mbstring, openssl, zip, gd, pcntl (for Horizon).

Node.js must stay installed in production, with the dependencies from package.json: the MJML editor uses it to render e-mails as they are sent.

Direction	For
Inbound 443	Interface, API, public pages, tracking pixels and links, provider feedback.
Inbound 2525	Only if you open the SMTP relay to other machines.
Outbound 443	Provider APIs, RSS feeds, outgoing webhooks, link checking.
Outbound 587 or 465	When a provider is wired up over SMTP.
DNS	Checking the sending domains (SPF, DKIM, DMARC).

Lekalao has to be reachable from the internet over HTTPS: subscribers click its links, and providers send it bounces and complaints.

The figures below are starting points; sending depends mostly on the rate your providers accept.

Size	Server	Sending workers
Up to 50,000 subscribers	2 vCPU, 4 GB, everything on one machine	3 to 5
Up to 500,000 subscribers	4 vCPU, 8 GB; PostgreSQL preferably on its own	10
Beyond that	Database and Redis of their own, several Horizon servers	As your providers allow

Leave disk room for the database: every e-mail sent leaves a row, and every open or click another one, kept 365 days by default.