Deliverability

SPF, DKIM, and DMARC get Blindrelay to accept your mail — inbox placement still depends on content, links, and gradual warmup. Use this page with Connection test (sign-in required) , the API reference, and live platform SMTP rates on System status. For reputation isolated after warmup and inbound aliases, see dedicated IP.

New domain warmup

• Week 1: Low volume to engaged recipients only (password resets, account confirmations). Target under 500 messages/day.
• Week 2: Double volume if bounce rate stays under 2% and complaint rate under 0.05%.
• Week 3+: Scale toward steady-state quota. Avoid sudden 10× spikes.

Prefer a production subdomain over dev.* for confidence checks. First messages to a mailbox can land in Spam or Promotions even when authentication passes — mark Not spam to help future sends.

Links in message bodies

• Never put localhost, *.localhost, or plain http:// login links in production sends — mailbox providers treat them as phishing.
• CTA hosts should share the same registrable domain as your From address.
• Always send https links in production. Blindrelay derives a plain-text part when you send only html; pass your own text for full control.
• Publish the recommended bounce.<your-domain> CNAME from the domain page so bounces use your domain and SPF aligns with your From address.

One-click unsubscribe

Every message with an unsubscribe or email-preferences link (newsletters, digests, reminders, product updates) should carry it as RFC 8058 headers too. Gmail and Yahoo then show their own Unsubscribe button next to the sender instead of leaving “Report spam” as the way out. Pass both in the headers field of POST /v1/send, with the same signed per-recipient URL as the footer link:

"headers": { "List-Unsubscribe": "<https://example.com/unsubscribe?u=…&token=…>", "List-Unsubscribe-Post": "List-Unsubscribe=One-Click" }

• The URL must accept POST (form body List-Unsubscribe=One-Click) with no sign-in, no confirmation page and no CSRF check, be idempotent and answer 2xx.
• A GET on the same URL only shows a confirm button that sends that POST: mail security scanners open every link in a message, so a GET that unsubscribes opts people out without them knowing.
• Leave both headers off strictly transactional mail (sign-in links, receipts, security alerts) and off mandatory notices that still arrive after an unsubscribe — the header promises an opt-out you would not honour.
• Blindrelay passes both headers through unchanged and covers them by its DKIM signature. Don't set From, To, Subject, Date, Message-ID or Return-Path in headers: Blindrelay sets them itself and ignores yours.
• Together with the bounce.<your-domain> CNAME above, SPF, DKIM and DMARC all align with your From domain — what Gmail and Yahoo check before they trust the header.

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