SignerRelay

SignerRelay is a web app + lightweight SMTP relay that adds DKIM signatures on behalf of systems that either can’t sign (legacy apps, printers, CRMs, on-prem tools) or are too painful to configure (no DNS access, rotating keys, multiple domains). You point your application to SignerRelay as its outbound SMTP, verify your domain(s), publish the provided DKIM DNS records, and the service signs mail with the correct selector and key. It includes per-sender/domain routing rules, safe defaults (no open relay), and deliverability checks to confirm alignment with SPF/DMARC. This is not a magic deliverability booster—if your sending reputation is bad, it won’t fix that—but it removes a common operational bottleneck: getting consistent DKIM across fragmented senders. The product lives or dies on reliability, clear audit logs, and painless onboarding for non-experts.