January 22, 2019

The Ultimate Email Hosting Glossary

Despite the rise of messaging solutions such as Slack, WhatsApp and Facebook Messenger, email is still an indispensable tool in our day-to-day lives. This is evidenced by The Radicati Group’s prediction in 2018 that 333 billion emails will be sent per day by year-end 2022. Even Slack’s co-founder Stewart Butterfield said in The Verge in 2014 that, “There isn’t really an alternative [to email]. Sometimes people will have Facebook messenger turned on, but 99 percent of the time if you’re sending a message to a human you don’t know well, you’re using email”.

But running email hosting systems is not easy…

Telcos and hosting providers don’t always find it easy to run customer email systems when it’s not their core area of expertise. The task of delivering modern, instant-sync, email experiences that run reliably 24/7, takes a lot of hard work behind the scenes.

There’s a lot of terminology to learn…

Newcomers to the field of email hosting are often slowed down by the amount of terminology to learn. From reverse DNS lookups to DDoS attacks, MX records to Joe Jobs, phishing to greylisting, SSL to TLS, 2FA to E2EE and more, to respond quickly to email hosting issues, you need to know your terminology.

To help, we’ve put together The Ultimate Email Hosting Glossary…

After 20 years of delivering reliable email solutions to telcos and hosting providers around the globe, we’ve come across hundreds of email terms. Over time, some terms have come and gone, but we’ve compiled what we think are currently the top 100 email hosting terms that telcos and hosting providers need to know. True, our glossary can’t help you run a customer email system, but it help give you (or your new team members) a great foundation from which to build your email hosting knowledge and point you in the right direction.


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Email Hosting Definitions

Here’s a sample of what’s inside our glossary:


Two-factor authentication (2FA), otherwise known as two-step verification or dual- factor authentication, is a security process that requires the user to verify their credentials with two different authentication factors (e.g. a password plus either a security token or a fingerprint).

Bayesian Filter

A Bayesian filter is a program that uses Bayesian logic to evaluate the header and content of an incoming email message and determine the probability that it constitutes spam. If an email message scores too highly in Bayesian spam points, it is either delivered to a junk folder or rejected completely.

Branded Email Hosting

Branded email hosting (or white label email) refers to the ability to prominently display a company’s branding on hosted webmail accounts.

DDoS Attack

A distributed denial of service (DDoS) attack is when a system is attacked and overwhelmed with data from multiple machines (sometimes upwards of hundreds of thousands) distributed across the internet. The systems flood the target with superfluous requests from many different sources so legitimate requests cannot be fulfilled.


End-of-life (EOL) email refers to the final stages of an email  product’s existence. This means that the software will no longer be improved or actively maintained. Organisations are not advised to use EOL email products, because they pose a security risk and leave an organisation more vulnerable to hackers.


Internet Message Access Protocol (IMAP) is a standard that was designed to allow multiple email clients to manage the same email account by maintaining the stored email on the server, rather than downloading messages directly to any one email client. IMAP is defined by RFC 3501.


JSON Meta Application Protocol (JMAP) is a protocol for synchronising data between a client and a server. Data includes, but is not limited to, email, calendars and contacts. JMAP is optimised for mobile and web environments and its goal is to provide a consistent interface for all data types.

Joe Job

Joe Job is an industry term for forged email spam. In order to hide their identity, the spammer or hacker fakes a genuine email address.


The Mail Abuse Prevention System (MAPS) provides antispam support by maintaining a Domain Name System-Based Blackhole List (DNSBL) or Real-time Blackhole List (RBL). This is essentially a list of locations on the internet reputed to send email spam.

MX Record

The mail exchanger (MX) record allows a single domain to run multiple mail servers. It does this by specifying which mail server is responsible for accepting the recipient’s incoming message.


A mail delivery agent (MDA), also known as a message delivery agent or local delivery agent, is the agent responsible for the delivery of emails to a local recipient’s mailbox.


A mail transfer agent (MTA), also known as a message transfer agent, is a type of software application that forwards inbound and/or outbound mail directly to the recipient.


A mail user agent (MUA), also known as an email reader, is a type of email client or software that uses collaborative computer environments to access and manage emails.

Multi-Part MIME

A multipart Multipurpose Internet Mail Extension (MIME) refers to emails that are sent containing both HTML and text formats. When a user receives a multi-part message, their device will automatically render to the format that the system has been set to show – either HTML or text.


Post Office Protocol (POP) is an application- layer internet standard protocol used to retrieve email from a server. The latest version, POP3, is defined in RFC 1939.


Role-based access control (RBAC) limits network access based on the user’s role within the company, so the user cannot operate beyond their jurisdiction.

Reverse DNS

A reverse DNS lookup matches an IP address to a domain name. This is different to a standard DNS lookup which matches the domain name to an IP address. Reverse DNS is a process for catching and preventing spammers with invalid IP addresses.


Simple Mail Transfer Protocol (SMTP) is an internet standard for electronic mail (email) transmission. It is a plaintext protocol, so you can just type commands from your keyboard and send an email. First defined by RFC 821 in 1982, it was updated in 2008 with Extended SMTP additions by RFC 5321, which is the protocol used widely today.


The Sender Policy Framework (SPF) is a protocol that prevents email forgeries, by placing a strip of code within the email sender’s DNS information. That way, the incoming mail server can simply interpret the SPF record to authenticate the sender’s identity, before it reaches the recipient. SPF addresses the vulnerability of the SMTP email protocol, which does not have any authentication capabilities of its own.


Web Distributed Authoring and Versioning (WebDAV), also abbreviated as DAV, is a protocol that facilitates collaborative authoring and editing between remote users over the web. CardDAV (an address book client/server protocol) and CalDAV (a calendar client/ server protocol) are extensions of WebDAV.


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New to atmail?

With 20 years of global, white label, email expertise serving telecommunications and hosting providers across every continent, you can trust us to deliver white label, email solutions that are stable, secure and scalable. We power 170 million mailboxes and offer user-friendly, cloud hosted email with 99.99% uptime and your choice of US or (GDPR compliant) EU data centres. Or, if you want to stay in-house, we offer on-premises webmail and/or mail server options. For more information about how we can help, please contact us here.

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