Show Google Postmaster Tools and Microsoft SNDS reputation data on the dashboard #76

Background

Delivery rate is a vanity metric: an ESP can report 99% "delivered" while mail lands in spam. MailCheap is about to publish open delivery-rate metrics (Marc Lou, 18 Oct 2026, 99.2% delivered), and Robby Frank replied that inbox placement is the only number worth showing (x.com/RobbyFrank/status/2111784068300042242). Senders switching from beehiiv also worry about reputation and warm-up on a new sending setup (see #67).

SendLit today shows sends, opens, clicks, bounces and complaints, but nothing about how mailbox providers rate the sender's domain or IPs. Google Postmaster Tools and Microsoft SNDS (Smart Network Data Services) both expose that reputation data for free.

Proposed fix

• Per team, let the sender connect Google Postmaster Tools (OAuth, Postmaster Tools API v1) for each verified sending domain, and pull daily domain reputation, IP reputation, user-reported spam rate, SPF/DKIM/DMARC pass rates and delivery errors.
• Let the sender connect Microsoft SNDS (automated data access key) for their dedicated IPs, and pull daily filter result (green/yellow/red), complaint rate and spam-trap hits.
• Show a "Reputation" card on the team dashboard next to the deliverability report (Deliverability report, mailbox-provider breakdown and subscriber growth chart #39), with a 30-day trend and alerts when Gmail spam rate is above 0.1% (warning) or 0.3% (Google's bulk-sender limit), or when domain reputation drops to Low/Bad or SNDS goes red.
• Link these signals to the warm-up guide and daily caps (Day-one warm-up answer: warm-up guide and self-serve daily send caps for new domains / SES accounts #67) and the auto-pause on bounce/complaint rates (Auto-pause broadcasts and sequences on high bounce or complaint rates #25).
• Docs page on how to verify a domain in Postmaster Tools and request SNDS access.

Acceptance criteria

• A team can connect Google Postmaster Tools via OAuth and see daily reputation, spam rate and authentication pass rates per sending domain
• A team can add an SNDS access key and see daily IP status and complaint rate
• The dashboard shows a 30-day trend for both, with an empty state that explains how to connect them
• Alerts fire (in-app and email) for Gmail spam rate above 0.1% / 0.3%, domain reputation Low/Bad, or SNDS red
• Data refreshes daily via a background job; tokens are stored encrypted
• Docs page published for setup

Related: #39, #67, #25, #4