How can I determine the ISP or mailbox provider of an email address?
Summary
What email marketers say9Marketer opinions
Email marketer from Mailjet shares that they provide information about the recipients ISP/Mailbox Provider when using a dedicated IP. This is because it is beneficial to split emails by provider, e.g., Gmail, Hotmail, Yahoo etc to gain optimal deliverability.
Email marketer from Medium responds to the question. You can utilize email marketing tools or services that offer subscriber information, including location and ISP details. These tools often use IP address geolocation and other data to enrich subscriber profiles.
Email marketer from Email Hippo explains that email append services which often provide extra data such as demographics, also append an email address's ISP or mailbox provider.
Email marketer from Email Geeks shares a method to identify the ISP/mailbox provider of an email address by looking up the domain's MX records, then the MX's A records, then the A's PTRs, and optionally whois the IPs, grouping by commonalities.
Email marketer from Quora responds to the question. You can identify the host of an email address by looking at the part after the @ symbol. The host is typically also the ISP. Do an IP lookup for the host to determine the email address's location and network provider.
Email marketer from Reddit suggests using email validation APIs (like AbstractAPI, Kickbox, or ZeroBounce) to get information about an email address, including deliverability status, whether it's a disposable email, and sometimes the provider. These tools perform various checks, including DNS lookups and SMTP verification.
Email marketer from Email Geeks shares to check `*.<http://protection.outlook.com|protection.outlook.com>` and `*.<http://google.com|google.com>` for MX Lookups to identify Microsoft365 vs. Google Workspace addresses.
Email marketer from LinkedIn suggests using an email validation service to get the ISP and mailbox provider of a user. This will return additional details associated with an email address.
Email marketer from Stack Overflow explains you can't reliably determine the *ISP* of an email address. You can only determine the *mail server* the domain uses by looking up the MX record. The ISP hosts the domain but is not necessarily the mail provider.
What the experts say3Expert opinions
Expert from Word to the Wise shares that reverse DNS lookups can help identify the organization responsible for an IP address. While this doesn't directly give you the "ISP", it can reveal the company or entity operating the mail server, which can often be a large ISP or a corporate mail infrastructure.
Expert from Spam Resource explains that determining the email provider often involves looking at the domain name after the '@' symbol. For more complex scenarios, performing a DNS lookup, specifically querying the MX records, can reveal the mail servers responsible for handling email for that domain. These MX records will often indicate the actual provider, even if the domain is custom.
Expert from Email Geeks shares she has a SQL function that does DNS lookups on the MXs, and a SQL script that classifies the raw MXs, splitting out Google domains (gmail-smtp-in.l.google.com, gmr-smtp-in.l.google.com, googlemail.com, aspmx.l.google.com, psmtp.com) and Microsoft domains (olc.protection.outlook.com, mail.protection.outlook.com, mail.outlook.com).
What the documentation says3Technical articles
Documentation from MXToolbox explains that their MX Lookup tool allows you to instantly check a domain's MX records. This provides information about the mail servers responsible for handling email for that domain.
Documentation from Microsoft Learn shares that you can use the Get-DnsClient cmdlet in Powershell to query DNS records, including MX records. This allows you to programmatically determine the mail servers for a given domain.
Documentation from Google Workspace Admin Help explains that MX records specify the mail servers responsible for accepting email messages on behalf of a domain name. You can look up the MX records to see where a domain's email is routed. Example: google.com will show the google mail servers