What are Postmaster Tools?

Postmaster Tools is what mailbox providers give serious senders so you can see how they're treating your mail. Right now, only Gmail offers a real one (Google Postmaster Tools). Microsoft has SNDS, which is similar in spirit but more limited. Yahoo offers Yahoo Sender Hub for sender reputation data.

What Google Postmaster Tools shows you

• Domain reputation. High / Medium / Low / Bad. The headline metric. Drives whether you land in inbox or Promotions or Spam at Gmail.
• IP reputation. Same scale, applied to your sending IPs. More relevant if you're on a dedicated IP than on shared.
• Spam rate. Percentage of recipients who marked your mail as spam. Stay under 0.1%.
• Authentication. Pass rates for SPF, DKIM, and DMARC. Anything below ~99% is usually a config problem.
• Encryption. Percentage of mail sent over TLS.
• Delivery errors. Why Gmail rejected or deferred messages.

What it doesn't show

• Other providers. Outlook, Yahoo, and corporate filters are invisible here.
• Per-recipient detail. You see aggregate rates, never which individual recipient complained or bounced.
• Real-time data. Most metrics lag by a day or two.
• Low-volume reality. If you're sending under a few thousand messages a day to Gmail, you'll often see "no data available" because Google needs statistical signal to evaluate.

How to actually use it

Set it up before you need it. The data only starts accumulating once you're verified, so don't wait until you have a deliverability fire to add the TXT record. Check it weekly, not daily. Reputation moves on a multi-day timescale, so daily checks just mean you'll panic at noise.

If you want a single view across Gmail, Microsoft, and the other providers Postmaster Tools doesn't cover, Review My Emails stitches them together so you're not switching dashboards.