go-notification

The SMTP driver — when to use it, what ports work, and the Gmail app-password walkthrough.

Cloud providers block SMTP ports

GCP — Port 25 blocked permanently, cannot request unblock.
AWS EC2 — Port 25 blocked by default, unblock requests often denied.
DigitalOcean — Port 25 blocked for all new accounts.
Azure — Port 25 blocked.

Port 587 (STARTTLS) usually works, but some providers restrict it too.

If you're deploying on cloud, use Mailgun, SendGrid, or SES instead of SMTP.

When to use SMTP

On-premise / bare-metal servers.
Corporate mail servers (Exchange, Postfix).
Self-hosted mail (Mailcow, iRedMail, Mail-in-a-Box).
Local development with Mailhog or Mailpit.
Non-restrictive hosts (Hetzner, OVH).

Setup

main.go

import "github.com/gopackx/go-notification/channel/mail/smtp"

notifier.RegisterChannel("mail", smtp.New(smtp.Config{
    Host:     "smtp.gmail.com",
    Port:     587,
    Username: "user@gmail.com",
    Password: os.Getenv("SMTP_PASSWORD"),
    From:     "noreply@example.com",
    FromName: "My App",
    TLS:      true,
}))

Gmail app password

Gmail won't accept your regular password for SMTP. You need an app password:

Enable 2-Step Verification on your Google account.
Go to https://myaccount.google.com/apppasswords.
Create a new app password, label it e.g. "go-notification".
Paste the 16-character password into SMTP_PASSWORD.

Configuration reference

Field	Type	Required	Description
`Host`	`string`	yes	SMTP server hostname (e.g. `smtp.gmail.com`).
`Port`	`int`	yes	Usually `587` for STARTTLS, `465` for implicit TLS, `25` for plain.
`Username`	`string`	yes	SMTP auth username.
`Password`	`string`	yes	SMTP auth password or app password.
`From`	`string`	yes	Default sender address.
`FromName`	`string`	no	Display name for the sender.
`TLS`	`bool`	no	Use STARTTLS on port 587. Default: `true` when port is 587.
`Timeout`	`time.Duration`	no	Connection + send timeout. Default: `30s`.

Troubleshooting

connection refused — wrong host/port, or firewall / cloud provider blocking.
EOF after HELO — TLS required but TLS: false. Set TLS: true.
535 5.7.8 — bad credentials. For Gmail, you need an app password, not your account password.
Works locally, fails in prod — your cloud provider is almost certainly blocking port 25/587. Switch to an API driver.