Why do Hetzner and DigitalOcean block port 25 on VPS servers?

Cloud providers block TCP port 25 outbound to prevent compromised virtual servers and rogue bots from dispatching spam across the internet. Unblocking port 25 requires strict identity verification and is often rejected. SadaSend operates dedicated pre-warmed European mail relays that accept mail over authenticated port 587 (STARTTLS), completely bypassing VPS firewall blocks.

Can I use Coolify with SadaSend on the free plan?

Yes. SadaSend provides 6,000 free emails every month with zero credit card required. This is ideal for Coolify server notifications, deployment alerts, and staging environments.

What is the difference between port 587 and port 465 in Coolify?

Port 587 is the standard RFC 6409 mail submission port that starts in plain text and upgrades to encrypted TLS via STARTTLS. Port 465 uses implicit SSL/TLS from the initial socket connection. SadaSend supports both ports, but port 587 with STARTTLS is recommended for Coolify.

Do I need to configure reverse DNS (rDNS / PTR) on my Coolify VPS?

No. When routing through SadaSend SMTP relay, all external delivery to Gmail, Microsoft 365, and Yahoo originates from SadaSend pre-warmed IPs with verified PTR records and European infrastructure in Germany (EU). You only configure standard SPF and DKIM DNS records on your domain.

How does SadaSend protect my Coolify apps from email bounces?

SadaSend includes an in-flight Pre-Send Bounce Shield that validates recipient syntax, disposable burner domains, and mailbox reachability before the message is dispatched to destination mail exchanges, protecting your domain sender reputation.

DevOps & Self-Hosted Integration

Coolify SMTP Relay & Transactional Email

Cloud VPS providers like Hetzner, DigitalOcean, and OVH permanently block outbound port 25, preventing self-hosted Coolify instances from sending alerts and auth emails. SadaSend provides authenticated port 587 STARTTLS relay with pre-warmed European IPs and 6,000 free monthly emails.

Get Free SMTP Credentials Check Cloud VPS Port 25 Status 2-Minute Setup Steps

The Port 25 Firewall Block

Why Self-Hosted Coolify Fails to Send Email on Cloud VPS

Major hosting providers filter outbound TCP port 25 to prevent spam. SadaSend bypasses firewalls using authenticated port 587 STARTTLS.

Hetzner CloudBlocked by Default

Port 25 outbound is filtered on all new accounts. Unblock tickets require identity verification, 30+ day account history, and are frequently rejected.

SadaSend Solution:

Instant delivery over port 587 with STARTTLS encryption. Zero waiting periods.

DigitalOceanPermanently Blocked

Port 25 is blocked on all Droplets created after June 2022. Support policy strictly refuses to unblock port 25 for transactional sending.

SadaSend Solution:

Authenticated ESMTP submission on port 587. Bypasses Droplet firewall rules.

OVHcloud & ScalewayThrottled & Filtered

Port 25 traffic is subject to anti-spam heuristics and rate-limiting. Outbound messages without strict PTR/rDNS fail silently.

SadaSend Solution:

Dual-DKIM (RSA + Ed25519) signing from sovereign Germany (EU) infrastructure.

Homelab & Residential ISPsISP Firewall Drop

Almost all consumer ISPs (Comcast, Deutsche Telekom, Vodafone) drop outbound TCP port 25 packets to prevent botnet spam.

SadaSend Solution:

Encrypted submission over port 587 works seamlessly across home networks.

Production Gateway

Coolify Transactional Email Settings Reference

Copy and paste these exact connection values into your Coolify server settings panel.

Setting Name	Recommended Value	Technical Specification
Enable Transactional Email	`Toggle ON`	Enables external SMTP routing across your Coolify server instance.
SMTP Host	`smtp.sadasend.com`	SadaSend high-performance European ESMTP relay gateway.
SMTP Port	`587`	Standard submission port using authenticated STARTTLS encryption (RFC 3207).
SMTP Security	`STARTTLS (or TLS)`	Encrypts email contents and credentials in transit before mail submission.
SMTP User	`apikey`	Standard username identifier for all SadaSend SMTP connections.
SMTP Password	`your_sadasend_api_key`	Your production API key generated in the SadaSend dashboard.
From Address	`notifications@yourdomain.com`	The verified domain address configured in your SadaSend dashboard.
From Name	`Your Coolify App`	The human-readable sender name displayed in recipient inboxes.

Ready-to-Paste Configuration Snippets

Drop these configurations directly into Coolify environment variables or Docker containers.

BASH

# Coolify Application Environment Variables (.env)
# Compatible with Laravel, Ghost, Plausible, Nextcloud, and custom Docker containers

MAIL_MAILER=smtp
MAIL_HOST=smtp.sadasend.com
MAIL_PORT=587
MAIL_USERNAME=apikey
MAIL_PASSWORD=sada_live_your_api_key_here
MAIL_ENCRYPTION=tls
MAIL_FROM_ADDRESS=notifications@yourdomain.com
MAIL_FROM_NAME="Coolify Production"

Fast Setup

Step-by-Step Setup Guide in Under 2 Minutes

From zero to verified live delivery across your self-hosted instances.

Generate your SadaSend SMTP Credentials

Create a free SadaSend account, add your custom domain (e.g. yourdomain.com), and copy your production API key from the Keys dashboard.

Navigate to Coolify Transactional Email Settings

In your Coolify console, click on Settings in the left sidebar, then select the Transactional Email tab.

Enter smtp.sadasend.com and Port 587

Toggle Enable Transactional Email to ON. Set Host to smtp.sadasend.com, Port to 587, Username to apikey, and Password to your SadaSend API key.

Send a Live Test Email and Verify Delivery

Click Send Test Email. Your test message delivers in under 150ms. Check the SadaSend Live Logs dashboard to inspect headers and delivery status.

Pre-Send Bounce Defense & EU Sovereignty

Protect your VPS and domain sender reputation

Running your own mail server on a VPS often results in Gmail or Microsoft dropping emails into spam due to missing PTR records or dirty IP ranges. SadaSend relays messages from pre-warmed European IPs in Germany (EU), verified with Dual-DKIM and live SPF alignment.

Start with 6,000 Free Emails

Frequently Asked Questions (Coolify & SMTP Relay)

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