A cold email lands in spam for a small set of boring reasons. The painful part is that the sending tool can still show a green mailbox while several of them are already true.
Authentication that receivers actually check
SPF says which servers may send for the domain. DKIM proves the message was signed by a key you published. DMARC tells receivers what to do when those two fail, and whether the visible From domain aligns with them.
If SPF is missing, duplicated, or ends in +all, a lot of filters stop trusting the domain. If DKIM is missing, the message is unsigned. If DMARC is missing or p=none, you are not asking anyone to quarantine spoofed copies of your domain, and some receivers treat that as a reason to be cautious with cold mail.
Inbox Watch's free checker reads those records directly. It does not turn them into a score.
The domain or the sending IP is listed
NordSpam, PSBL, and Mailspike's block codes are the lists this checker treats as a reason to stop. A listing can happen after a bad list, a compromised mailbox, or a neighbor on a shared IP. Instantly and Smartlead do not query those lists for you on every send. A warmup "health score" is a different measurement, usually based on seed mailboxes, not on whether a DNSBL currently lists the host. Spamhaus still matters to mailbox providers. This checker does not query it. The result page links to Spamhaus's own lookup.
Bounces and replies moved, quietly
A bounce rate that climbs past a few percent means the list is bad or the domain is being refused. A 7-day reply rate that falls under half of that domain's own baseline often means the mail is no longer being seen by people, even when opens still look fine. Opens are easy to inflate. Replies are not.
Compare a domain with itself. A 2% reply rate is a collapse for a domain that used to do 6%, and it is normal for a domain that has always done 2%.
What to do first
- Run the domain through the checker and fix SPF, DKIM, and DMARC before you change copy.
- If a major blacklist lists it, stop sending on that domain and request delisting. Do not "push through" the week.
- If bounces are up, rest the domain and clean the list. New copy will not fix a refusal.
- If replies fell off a real baseline and authentication is intact, rest the domain and cut volume. Replacement is for domains that are listed, unsigned, or bouncing hard.
Inbox Watch sends that keep / rest / replace call every Monday, using the same rules it uses for alerts.