IP Address Info - Lookup Location, ISP and Reverse DNS

Why IP address info matters for email deliverability

• ISP and hosting type - Mail sent from a residential ISP IP is often blocked or filtered. Mail from a reputable hosting or email provider has higher trust.
• ASN (Autonomous System Number) - Large sending platforms and ESPs have known ASNs. Receiving mail servers use ASN reputation as a signal for filtering.
• Reverse DNS (PTR) - A missing PTR record or one that does not match the sending hostname is a major deliverability red flag. Many mail servers reject email from IPs without a valid PTR record.
• Country of origin - Some mail servers apply stricter filtering to email from certain regions. If your sending IP geolocates unexpectedly, it may indicate a misconfigured or shared relay.

FAQ

How do I find my mail server's sending IP address?

Look at the email headers of a message you sent. The Received: headers show the IP addresses the message passed through. The outermost Received: header (closest to the bottom) shows the original sending server IP. You can also use the MX Lookup to find your inbound mail server and then look up its IP with an A record lookup.

Why does my mail server IP show as a hosting IP?

Most email sending platforms and self-hosted mail servers run in data centers. A data center or hosting IP is normal for legitimate email - ESPs like Mailgun, SendGrid, Postmark, and Amazon SES all use hosting IPs. What matters is whether the IP has a good sending reputation and is not on a blacklist.

Does IP geolocation affect spam filtering?

It can contribute as one of many signals, but it is rarely the primary factor. Authentication (SPF, DKIM, DMARC), sender reputation, content quality, and engagement rates matter far more. Geographic filtering is more common for specific industries or high-fraud regions.