Knowing your current IP reputation and whether you are on any blacklists is essential for diagnosing deliverability problems and tracking improvement over time. This article covers every tool available for checking IP reputation — free and paid — with step-by-step instructions for the most useful ones.
Finding Your Sending IP Address
Before checking your reputation, you need to know which IP address MigoSMTP is using to send your email. You can find this in the email headers of any delivered message:
- Open a delivered email in your inbox.
- View the full email headers (in Gmail: three-dot menu → Show original; in Outlook: File → Properties).
- Look for the
Received: fromheader line near the top — the IP in square brackets is the sending IP (e.g.Received: from smtp-out.migosmtp.com [203.0.113.42]). - Alternatively, check the
X-Originating-IPorX-Sender-IPheader if present.
Shared IP note: On the default shared IP plan, MigoSMTP may rotate between multiple IPs from its shared pool. Check the headers of several recent emails to identify the range of IPs being used. For dedicated IP customers, the IP is fixed and consistent.
Reputation Checking Tools — Complete Reference
| Tool | URL | What It Checks | Cost |
|---|---|---|---|
| MXToolbox Blacklist Check | mxtoolbox.com/blacklists.aspx | Checks your IP against 100+ blacklists simultaneously; shows which lists you are on and how to delist | Free |
| Sender Score (Validity) | senderscore.org | 0–100 aggregate reputation score; shows 30-day trend; data used by many ISPs and filtering services | Free |
| Google Postmaster Tools | postmaster.google.com | Gmail's view of your domain AND IP reputation; spam rate; authentication; delivery errors — the most accurate Gmail-specific data available | Free |
| Microsoft SNDS | sendersupport.outlook.com | Outlook/Hotmail's Smart Network Data Services — delivery data, complaint rates, and spam trap hits specific to Outlook users | Free |
| Talos Intelligence | talosintelligence.com/reputation_center | Cisco's threat intelligence reputation — used by Cisco IronPort gateways in enterprise environments; Good / Neutral / Poor rating | Free |
| Spamhaus IP Lookup | check.spamhaus.org | Checks against Spamhaus ZEN (combined blocklist); if you are on SBL, XBL, or PBL this tool shows it — Spamhaus is the most influential blocklist globally | Free |
| Barracuda Reputation Lookup | barracudacentral.org/lookups | Checks the Barracuda Reputation Block List (BRBL) — widely used by Barracuda spam filters in enterprise email gateways | Free |
| MultiRBL | multirbl.valli.org | Comprehensive blacklist check across 200+ DNSBL, RHSBL, and URI blacklists in one query | Free |
| GlockApps Inbox Insights | glockapps.com | Reputation monitoring + inbox placement testing across multiple ISPs; continuous monitoring with alerts | Paid (free trial) |
Step-by-Step: Running an MXToolbox Blacklist Check
- Go to mxtoolbox.com/blacklists.aspx.
- Enter your sending IP address in the search field.
- Click Blacklist Check.
- Results appear within 15–30 seconds — a list of all checked blacklists with status for each.
- Any red Blacklisted entries require immediate action.
- Click on any blacklisted entry for details about why you are listed and a link to the delisting request form.
Step-by-Step: Setting Up Microsoft SNDS
- Go to sendersupport.outlook.com/snds/.
- Sign in with a Microsoft account.
- Click Request Access and enter the IP address or IP range you want to monitor.
- Microsoft sends a verification email to the postmaster address of the IP owner. For MigoSMTP shared IPs, contact Rackwave support to assist with SNDS registration.
- Once verified, SNDS provides daily data on your IP's delivery rates, complaint rates, and spam trap hit information for Outlook.com users.
Interpreting Your Reputation Check Results
| Result | Severity | Immediate Action |
|---|---|---|
| Listed on Spamhaus SBL (spam source) | Critical | Stop all sending; investigate root cause; fix the issue; submit Spamhaus removal request |
| Listed on Spamhaus XBL (exploited systems) | Critical | Indicates server compromise or malware; full security audit required before delisting |
| Listed on Barracuda BRBL | High | Submit removal request at barracudacentral.org; improve sending practices |
| Listed on minor/low-traffic blacklist | Medium | Submit removal; lower priority than Spamhaus or Barracuda listings |
| Sender Score below 70 | Medium | Review negative factors; improve list quality and complaint rates; allow time for score to recover with clean sending |
| All checks pass; Sender Score above 90 | Healthy | Continue current practices; schedule regular monthly checks to detect any deterioration early |
Setting Up Regular IP Reputation Monitoring
Do not wait for deliverability problems to appear in your send metrics — check proactively:
- Weekly: Run MXToolbox blacklist check on your sending IPs.
- Weekly: Review Sender Score trend — is it stable, improving, or declining?
- Daily during warmup: Check Google Postmaster Tools IP reputation rating.
- Monthly: Full reputation audit across all tools listed above.
- Alert trigger: If delivery rate drops more than 5% in one day, immediately check all reputation tools.