Access Control List.

An ACL determines what networking traffic is allowed to pass and what traffic is blocked.

An ACL change is sometimes required to your company firewall in order to access our API.


Application Programmers Interface.

See Wikipedia - API Definition for more information.


Business To(2) Business

Business email hosting services are generally private, enterprise grade hosting services typically hosted in either private data centers or in cloud based infrastructure.

Business to business refers to the activity of businesses sending email to clients using business email addresses.


Business To(2) Consumer

Consumer email hosting providers are generally well known, mostly web based providers such as Hotmail, Yahoo, AOL, Gmail etc.

Business to consumer refers to the activity of businesses sending email to clients using consumer email addresses.

Verifying email addresses in consumer domains is generally more technically challenging than B2B

Block list



Binary Object Notation

See Wikipedia - BSON for further information.


Cross Origin Resource Scripting

Allows modern browsers to work with script (e.g. JavaScript) and JSON data originating form other domains.

CORS is required to allow client script such a JavaScript, jQuery or AngularJS to work with results returned from an external RESTful API.

See Wikipedia - CORS for more information.


Distributed Denial of Service

See Wikipedia - Denial-of-service attack for more information.


Disposable Email Address

There are many services available that permit users to use a one-time only email address. Typically, these email addresses are used by individuals wishing to gain access to content or services requiring registration of email addresses but same individuals not wishing to divulge their true identities (e.g. permanent email addresses).

DEA addresses should not be regarded as valid for email send purposes as it is unlikely that messages sent to DEA addresses will ever be read.


Domain Name System

At its simplest level, DNS converts text based queries (e.g. a domain name) into IP addresses.

DNS is also responsible for providing the MX records needed to locate a domains mail servers.

See Wikipedia - Domain Name System for more information.


DNS Block List

As an anti-spam measure, mail servers can use spam black lists to ‘look up’ the reputation of IP addresses and domains sending email. If an IP or domain is on a block list, the mail server may reject the senders email message.

See Wikipedia - DNSBL for more information.


Email Service Provider

A service that sends emails on your behalf.

See Wikipedia - Email service provider (marketing) for more information.

Free mail

Addresses served by popular B2C service providers such as Hotmail, Yahoo, Live, AOL, Gmail and so on.

Grey listing

A technique used in mail servers as an anti-spam technique. Sometimes also known as “deferred”, grey listing arbitrarily delays the delivery of emails with a “try again later” response to the client sending the email.

See Wikipedia - Grey Listing for more information.


Hypertext Transfer Protocol

See Wikipedia - Hypertext Transfer Protocol for more information.

IP address

Internet Protocol Address

See Wikipedia - IP Address for more information.

ISO 3166

International standard for country codes.

See Country Codes - ISO 3166 for more information.


JavaScript Object Notation

JavaScript Object Notation, is an open standard format that uses human readable text to transmit data objects consisting of attribute value pairs. It is used primarily to transmit data between a server and web application, as an efficient, modern alternative to XML.

See Wikipedia - JSON for more information.

License key

License key authentication is best for situations where simplicity is required and you can keep the key private. An ideal use case for key authentication would be for server based applications calling the RESTful API.

Click here to request a license key.




Mail Exchanger

The MX is a server responsible for email interchange with a client.


Non Delivery Report

A message that is returned to sender stating that delivery of an email address was not possible.

See Wikipedia - Bounce message for more information.

Office 365

Office 365 mail servers (e.g. are always configured with the catch all policy, accepting all emails sent to the domain and redirecting them to a central email box for manual inspection. Catch all configured servers cannot respond to requests for email address verification.

This does not affect our coverage of Hotmail, Live and Outlook mailboxes.


Protocol Buffers is a method of serializing structured data.

See Wikipedia - Protocol Buffers for more information.


Punycode is a way to represent Unicode with the limited character subset of ASCII supported by the Domain Name System.

See Wikipedia - Punycode for more information.


Representational state transfer

See Wikipedia - RESTful for further information.


Request for Comments

The principal technical development and standards-setting bodies for The Internet.

See Wikipedia - Request for Comments for further information.

Role address

A role address is a generic mailbox such as info@<domain>, sales@<domain> used by organizations to manage email messages of similar organizational types. For example, email messages sent to sales@<domain> can be routed to an organizations sales team where a team of sales people can deal with enquiries.

Role addresses allow collaborative working based on groups rathert than indiviidual mailboxes.


Service Level Agreement

See Wikipedia - SLA for more information and description of SLA.

See our Service Level Agreement.


Simple Mail Transport Protocol

SMTP is a protocol. It is the sequence of commands and responses between a client (the software sending an email) and server (the software receiving an email) that facilitates the sending and receiving of email between computer based email messaging systems.

Spam trap

Spam traps are email addresses used for the sole purpose of detecting spamming activities.

Spam traps are used by many block lists (DNSBL) to detect spammers.

For more information, see Wikipedia - Spam Traps.


TXT records associate arbitary and unformatted text with a domain. TXT records uses include Sender Policy Framework (SPF) and other domain validation applications.

For more information, see Wikipedia - TXT record.


e(X)tensible Markup Language

See Wikipedia - XML for further information.