Your sending platform's metrics tell you how many messages were accepted, opened and clicked. They don't tell you how many ended up in the spam folder, or what the receiving providers think of you. To get closer to that information there are the tools some large providers offer to senders. They are neither complete nor perfect, but they are the only direct view from the other side.
Google Postmaster Tools
Setup
Postmaster Tools works on the domain, not the IP. To activate it, you add your sending domain and prove you control it by publishing a TXT record in DNS. It is worth registering the domain used in From and, if different, the DKIM signing domain: data is attributed on the basis of authentication.
Charts appear only when daily volume to Gmail users is high enough. If you send a few dozen messages a day, you will often see empty panels: that isn't a configuration error, it is a minimum data threshold.
What to look at
The available sections have changed over time, but some data points are central:
- spam rate: the share of messages users reported as spam relative to those delivered to the inbox. It is the most important figure and must be kept very low;
- compliance status with sender requirements: authentication, DMARC alignment, one-click unsubscribe, PTR record, encryption;
- authentication: the percentage of messages passing SPF, DKIM and DMARC;
- encryption: the share of traffic received over TLS;
- delivery errors: rejections and throttling, with their reasons.
The spam rate needs careful reading. It is calculated on messages that reached the inbox, so a low value alongside falling volume can hide the fact that many messages are already going to spam, where they can no longer be reported.
Microsoft SNDS
Setup
SNDS, Smart Network Data Services, works on IP addresses. To access an IP's data you have to prove you are responsible for it: Microsoft sends an authorisation request to addresses linked to the IP, such as those in the registration data or an administrative address on the PTR record's name.
This has a practical consequence: SNDS is useful to those who run dedicated IPs or their own servers. If you use a platform's shared pool, you cannot register those addresses and must rely on the platform's own data.
What it shows
For each IP, day by day, SNDS typically reports:
| Data | Reading |
|---|---|
| messages and recipients | volume received from that IP |
| filter result | a colour indicator: green, yellow or red |
| complaint rate | share of messages reported as junk |
| trap hits | messages that reached spam traps |
| samples | example messages, useful for seeing what was sent |
An IP moving from green to yellow deserves immediate investigation; red means most of the traffic is being filtered. Trap hits are a particularly useful signal, because no other tool shows them so directly.
Alongside SNDS, Microsoft offers a complaint reporting programme that sends the sender a copy of messages users have marked as junk.
Other providers
Other providers also offer sender portals, with different data and access requirements. It is worth checking which are available for the domains best represented on your list: if a quarter of your subscribers use a particular provider, its data is worth as much as Gmail's.
From charts to actions
The tools are only useful if someone looks at them regularly and knows what to do. A simple routine:
- a weekly check of the main values, noting special sends, imports or configuration changes;
- comparison with your own metrics: a rise in spam rate that coincides with a new segment points to the cause;
- a compliance check after every change to DNS or the platform;
- alert thresholds: for example a spam rate above 0.1% for several consecutive days.
When the data worsens, the levers are almost always the same: reduce or suspend the least engaged segments, check where recent contacts came from, verify that unsubscribing works and is clearly visible.
In short
- Postmaster Tools works on the domain and is activated with a DNS TXT record.
- Gmail's spam rate is the most important figure, but it must be read alongside volume.
- SNDS works on IPs and is mostly useful to those running dedicated IPs.
- The trap hits shown by SNDS are a valuable and rare signal.
- The data only helps with a check routine and defined alert thresholds.
