Postmark

Postmark is opinionated — they only accept transactional mail and actively refuse marketing volume. That single choice is why they consistently top third-party deliverability tests.

Pricing

• Free trial — 100 emails/month (stays free forever if you don't exceed that).
• Paid — from $15/month for 10,000 emails.
• Per-message cost drops to around $1.25 per 1,000 on higher tiers.

https://postmarkapp.com/pricing has the current breakdown.

Setup

1. Sign up at https://postmarkapp.com.
2. Create a server (Postmark's term for a sending context) — typically one for Transactional and one for Broadcast.
3. Add and verify a sender signature (single address) or full domain auth (recommended).
4. Copy the Server Token from the server's API Tokens tab.

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

notifier.RegisterChannel("mail", postmark.New(postmark.Config{
    ServerToken: os.Getenv("POSTMARK_SERVER_TOKEN"),
    From:        "noreply@example.com",
    FromName:    "My App",
    MessageStream: "outbound",
}))

Configuration reference

Why Postmark

• Deliverability. If a user report "never got the email," Postmark is the fastest fix.
• Clear separation. Broadcast (marketing) and transactional live on different IPs and streams — a spam complaint on one won't poison the other.
• Bounce & complaint feedback comes back fast and structured.

Don't use Postmark for

• Bulk marketing. They will ask you to move it to their Broadcast stream or to a different vendor. Ignoring this gets your account suspended.
• High-volume low-value mail (signup notifications over millions/month at pennies each) — SES is cheaper.

Troubleshooting

• 422 Unprocessable Entity — almost always a missing or non-verified sender signature.
• Inactive recipient — Postmark suppresses previously-bounced addresses. Clear them from the dashboard or use a different address.
• Multiple streams confused — make sure MessageStream matches an actual stream on the server you're pointing at.