You're on a call with a developer and they mention "MX records." You nod. They say something about DKIM and IMAP. You nod again. The call ends and you Google all three. If you're running a SaaS and need privacy-focused analytics alongside your email setup, the terminology overlap can be overwhelming.

Sound familiar? Email hosting is one of those things every founder has to deal with but nobody actually explains. The documentation assumes you already know what a catch-all is. You don't. (You didn't. Now you will.)

This glossary covers the terms you'll actually encounter when setting up business email — no RFC references, no server admin jargon, just plain English.

MX Record

MX stands for Mail Exchange. An MX record is a DNS entry that tells the internet which server handles email for your domain.

When someone sends an email to you@yourdomain.com, their email server looks up your domain's MX record to find out where to deliver it. If you use Google Workspace, your MX records point to Google's mail servers. If you use JustEmails, they point to ours.

Here's the thing most founders miss: if you buy a domain and don't set up MX records, email to that domain goes nowhere. It doesn't bounce — it just disappears into the void. Set up your MX records.

You configure MX records wherever you manage your domain's DNS — usually your registrar (Namecheap, Cloudflare, GoDaddy) or a separate DNS provider. If you're also setting up call tracking for sales teams, you'll be in DNS a lot — get comfortable with it.

Mailbox

A mailbox is a real email account with storage, a login, and the ability to send and receive mail.

When you create jane@company.com and Jane can log in, read messages, and reply — that's a mailbox. Mailboxes take up storage space because the emails live somewhere.

This is different from an alias (see below). The distinction matters because some providers charge per mailbox. Google Workspace runs $84+/user/year. Microsoft 365 starts at $72+/user/year. JustEmails? $49/year flat for unlimited mailboxes — same price whether you have 2 or 200. I've seen agencies burn through hundreds a month on per-seat fees before realizing this.

Alias

An alias is a forwarding address that routes to a real mailbox. It doesn't store email itself.

Example: You create support@company.com as an alias pointing to jane@company.com. Emails to support@company.com land in Jane's inbox. But Jane can't log in as "support@company.com" — it's not a real account with storage, just a redirect.

Aliases are useful for:

Creating role-based addresses (sales@, billing@, hello@) without creating separate logins
Giving one person multiple addresses
Testing email flows without cluttering real inboxes

On most providers, aliases are either free or counted differently than mailboxes. On JustEmails, aliases are unlimited and free.

Catch-All

A catch-all is a mailbox that receives all email sent to addresses that don't exist on your domain.

Say you only have jane@company.com set up. Someone emails info@company.com by mistake. Without a catch-all, that email bounces. With a catch-all pointing to Jane's mailbox, she gets it anyway.

The upside: you never miss email due to typos or made-up addresses. The downside: spammers love catch-all domains. Once they figure out any random string @yourdomain.com works, they'll send to a8f39@yourdomain.com and you'll get it.

My take: enable catch-all early when your domain is new and unknown. Disable it later if spam becomes unmanageable. I learned this the hard way — left catch-all on for six months and my inbox became a landfill. Or use filtering, I guess, if you're more disciplined than me.

IMAP

IMAP (Internet Message Access Protocol) is a way for email clients to connect to your mailbox. It keeps your emails on the server and syncs them across all your devices.

When you add your work email to both your phone and your laptop using IMAP, they show the same inbox. Read an email on your phone, and it's marked as read on your laptop too. Delete it on one device, gone everywhere.

This is how most people should set up business email in 2026. Your mail client (Apple Mail, Outlook, Thunderbird, Gmail's "Check mail from other accounts") connects via IMAP, and everything stays in sync.

POP3

POP3 (Post Office Protocol version 3) downloads emails to your device and — by default — deletes them from the server.

This made sense in 1995 when server storage cost money and everyone used one computer. Today? Almost never what you want. If you check email with POP3 on your laptop, your phone won't see those messages because they're no longer on the server.

The only real use case: local archiving. Some businesses download all email to a local machine for compliance or backup purposes, using POP3 with "leave a copy on server" disabled. Everyone else should use IMAP.

SMTP

SMTP (Simple Mail Transfer Protocol) is how email gets sent. While IMAP handles receiving and reading, SMTP handles outgoing mail.

When you configure an email client, you'll usually enter two servers: an IMAP server (for receiving) and an SMTP server (for sending). Different ports, different credentials sometimes.

SMTP is also what transactional email services like Postmark, SendGrid, and the JustEmails API use under the hood. Your app connects via SMTP (or a REST API wrapper) and sends password resets, receipts, notifications. For development teams, tools like DevOS can help manage your local environment while testing email integrations.

SPF

SPF (Sender Policy Framework) is a DNS record that lists which servers are allowed to send email on behalf of your domain.

Without SPF, anyone can send email claiming to be from yourdomain.com — that's how spoofing works. With SPF, receiving servers check whether the sending server is on your approved list. If not, the email fails authentication and likely goes to spam (or gets rejected entirely).

An SPF record looks like this:

v=spf1 include:_spf.google.com ~all

That says "Google's servers are allowed to send as my domain; everyone else, treat with suspicion."

One rule: you can only have one SPF record per domain. If you use multiple email services (your hosting provider plus Mailchimp plus your app's transactional emails), combine them into one record. Multiple SPF records break everything.

DKIM

DKIM (DomainKeys Identified Mail) is a cryptographic signature attached to your outgoing emails.

Your email provider generates a private key (kept secret) and a public key (published in your DNS). When you send an email, the provider signs it with the private key. When the recipient's server receives it, they check the signature against your public key. If it matches, the email hasn't been tampered with.

DKIM is required by Gmail and Yahoo for any sender doing volume. Skip it and your emails go to spam. No negotiation. Every legitimate email provider sets this up automatically or gives you the DNS record to add — JustEmails handles SPF, DKIM, DMARC, and MTA-STS automatically, which frankly saves me from myself.

DMARC

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a policy that ties SPF and DKIM together and tells receiving servers what to do when authentication fails.

A DMARC record looks like:

v=DMARC1; p=reject; rua=mailto:dmarc@yourdomain.com

The p= part is the policy:

none: monitor only, don't block anything
quarantine: send failing emails to spam
reject: refuse delivery entirely

Start with p=none to see what's happening. Move to quarantine after a few weeks. Graduate to reject once you're confident all legitimate email passes. Jumping straight to reject will bounce your own emails if anything's misconfigured.

Per-Seat Pricing vs Flat-Fee

Per-seat pricing charges you for each user or mailbox. Google Workspace at $84+/user/year means 10 users costs $840+/year minimum. Microsoft 365 at $72+/user/year puts 10 users at $720+/year. The math gets ugly fast.

Flat-fee pricing charges a single price regardless of how many mailboxes you create. JustEmails charges $49/year — period. Ten mailboxes, fifty mailboxes, two hundred mailboxes. Same price. (Yes, really.)

The break-even math is obvious. If you have more than one user and don't need the productivity suite (Docs, Sheets, calendars), flat-fee providers save real money. Agencies managing client email across dozens of domains save thousands annually. Honestly, the per-seat model feels like a holdover from a different era — it made sense when storage was expensive, but it's 2026.

Per-seat makes sense when you're actually paying for a productivity platform and email is bundled. Flat-fee makes sense when you just need email. If you're running paid ads and watching every dollar (maybe using ClickzProtect to block click fraud), per-seat email costs add up fast.

Webmail

Webmail is a browser-based interface for checking email — like Gmail's web interface or Outlook.com.

Most email providers offer webmail alongside IMAP/SMTP access. You can use either or both. Webmail is convenient when you're on someone else's computer — though for real privacy, consider a dedicated browser. IMAP with a native app (Apple Mail, Thunderbird, Outlook desktop) is usually faster for daily work.

JustEmails includes webmail. So does Zoho, Fastmail, Google Workspace, and pretty much everyone else.

DNS Propagation

DNS propagation is the time it takes for DNS changes to spread across the internet.

When you update your MX records or add an SPF record, it doesn't happen instantly everywhere. Different DNS servers around the world cache records for different amounts of time. Propagation can take anywhere from 5 minutes to 48 hours, though modern registrars like Cloudflare usually propagate within minutes.

The practical implication: after changing DNS, your email might work immediately for some recipients and not others. This is maddening when you're trying to debug. Wait. Test. Wait more if needed. Resist the urge to change things again while it's propagating — you'll just make it worse.

TLS / Encryption in Transit

TLS (Transport Layer Security) encrypts email while it's moving between servers.

Think of it like HTTPS for email. The email content is encrypted during transmission, so someone intercepting the traffic can't read it. This is standard on every legitimate email provider in 2026.

TLS encrypts in transit. It doesn't encrypt email at rest (while stored on the server) unless the provider specifically offers that. Proton Mail encrypts everything end-to-end. Most providers — Google, Microsoft, JustEmails — encrypt in transit and at rest with server-side keys, meaning the provider can technically access the content.

For most businesses, TLS is enough. For highly sensitive communications, consider end-to-end encrypted providers.

Honorable Mentions

BIMI — Brand Indicators for Message Identification. Lets you display your logo next to emails in Gmail. Requires DMARC at p=reject plus a Verified Mark Certificate (costs money). Nice-to-have, not essential.

MTA-STS — Mail Transfer Agent Strict Transport Security. Forces TLS encryption when receiving servers talk to yours. Prevents downgrade attacks. Worth setting up if you're security-conscious.

PTR Record / Reverse DNS — Maps an IP address back to a domain name. Some receiving servers check that the sending server's IP has a PTR record matching the domain. Usually handled by your provider, not something you configure yourself.

Quick Verdict

If you remember one thing from this glossary: get your MX, SPF, DKIM, and DMARC set up correctly. Everything else is secondary.

Most email delivery problems aren't about which provider you use — Google, Microsoft, Zoho, JustEmails, Fastmail, whoever. They're about misconfigured DNS. A properly configured $49/year provider delivers email just fine. A misconfigured $800/year setup lands in spam. I've watched this happen.

The terminology isn't hard once you see it explained in plain language. Honestly, it took me embarrassingly long to learn most of this — I just nodded along in meetings for months. And now you have a cheat sheet. Check out our JustEmails blog for more guides like this. Go set up your records before you forget.

Frequently Asked Questions

What's the difference between a mailbox and an alias?

A mailbox stores emails and has its own login credentials — you can send and receive mail from it. An alias is just a forwarding address that routes to a real mailbox. Aliases don't store mail or have logins. Example: support@company.com (alias) could forward to jane@company.com (mailbox). On JustEmails, both are unlimited at $49/year.

Should I use IMAP or POP3 for my business email?

IMAP, almost always. IMAP syncs across devices — emails stay on the server and your phone, laptop, and tablet all show the same inbox. POP3 downloads emails to one device and can delete them from the server. The only reason to use POP3 is if you're archiving locally and never checking email anywhere else.

What does catch-all email mean?

A catch-all catches every email sent to any address @yourdomain.com that doesn't have a dedicated mailbox or alias. If someone emails typo@yourdomain.com by mistake, catch-all routes it to a mailbox you designate. Useful for small teams, but attracts spam if your domain is public.

Why does per-seat pricing matter for email hosting?

Per-seat pricing charges per user or mailbox — $6/user/month adds up fast if you have 10+ people. Google Workspace and Microsoft 365 use per-seat. Flat-fee pricing (like JustEmails at $49/year for unlimited mailboxes) charges one price regardless of how many mailboxes you create. For agencies or teams with lots of aliases, flat-fee saves significant money.

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Email Hosting Glossary for Non-Technical Founders (2026)