Email is the medium of business. It’s how requests, deals, and hires get started and made.

Most businesses live in their inbox, whether they like it or not. And that inbox is likely an Outlook inbox — over 3.7 million companies use Microsoft Outlook for email management.

Two main reasons for that:

1. Outlook is the default email client for Microsoft 365, a suite many businesses rely on (Excel, Word, Teams).
2. It offers enterprise-level security, compliance, and control (GDPR, HIPAA, encryption, granular user permissions).

However, like Word or Excel, Outlook was built mostly for enterprise solo use. It wasn’t built for collaboration, even as the world of business and email moved toward needing more of it.

In 2026, several tools meet the security and control standards of Outlook while offering more powerful inbox collaboration and coordination features suited for modern teams.

We’ll cover what to look for in an Outlook email client, introduce the six most popular third-party options, and break down their key differences.

Here are the key features we looked at for Outlook email clients:

• User interface and experience
• Security and privacy
• Customization options
• Collaboration features
• Productivity features
• AI-specific features

All options have desktop and mobile email apps and support IMAP, MAPI, and POP3.

We’ve also covered a range of price points, including free email clients.

Missive

Missive is a collaborative inbox for teams that run on email. It’s built with collaboration as a priority, featuring contextual in-email chat using @mentions, which eliminates the need for forwarding.

You can assign or watch emails, and every action is logged, giving you visibility into who did what and when.

Missive supports all email providers (Outlook, Gmail, Yahoo, Apple Mail) and you can have multiple accounts (personal and business) in the same interface.

Under the hood, Missive has a powerful automation engine. You can:

• Route emails from a specific sender to certain people or teams.
• Create a service level agreement (SLA) with notifications to hold your team to a response standard.
• Have AI read and understand the contents of an email to spot deadlines, label as urgent, and assign to a senior staff member for reply.
• Have AI read and understand the contents of an email to catch spam and automatically trash it.

From a security perspective, Missive meets the same standard as Outlook. SOC 2 Type II report, encryption of data at rest and in transit, GDPR compliant.

Pricing starts at $14/user/month on an annual plan.

One thing to note: if you use folders in Outlook, they’re called labels in Missive.

In the same way some teams prefer Google Docs to Word for its collaboration features (commenting, multi-player drafting), you may prefer Missive to Outlook if you find yourself hitting Reply All and Forward all the time.

Thunderbird

Thunderbird stands out as the only open-source email client on this list.

It’s a community-driven, free email client that’s been around for nearly two decades. With a thriving online community and an ecosystem of 1200+ add-ons (including AI-powered ones for drafting replies), it’s considered one of the best email apps for users who prioritize a free, open-source option.

If you’re looking for more collaboration functionality, Thunderbird’s collaboration features come mostly from third-party add-ons: things like mail merging and adding notes/comments to emails. Workable, but likely unreliable given the nature of third-party connections.

From an organization perspective, Thunderbird calls their version of “folders” tags. Functionally, they’re the same.

Thunderbird is privacy-forward with built-in filters for phishing/spam and remote image blocking. It doesn’t have SOC or ISO compliance certifications, because of its free and open-source nature.

Mailbird

Mailbird is for those who have too many email accounts. It’s known for its unified inbox, where you can flow multiple accounts into the same consolidated inbox view.

Mailbird doesn’t offer features related to collaboration or coordination. It’s a productivity improvement for Outlook power users who want to integrate popular apps into their email workflow and see all emails in one place.

From an AI perspective, Mailbird offers simple AI drafting through ChatGPT.

Of all the Outlook alternatives on this list, Mailbird has the most similar user experience to Outlook, including naming conventions (folders are folders, not labels or tags).

For security and compliance, Mailbird is GDPR compliant and does not have any external audits or certifications.

For pricing, Mailbird has a free version and a premium version at $4.99/user/month. There’s also a one-time payment option to buy the product outright at $49.50 (standard) or $99.75 (premium).

If you manage multiple Outlook accounts and need a unified inbox for all your emails, Mailbird might be a good fit.

eM Client

eM Client is similar to Mailbird. Most of its features are productivity-focused for individuals: shortcuts, watch/snooze, configurable layout.

The most unique and powerful feature in eM Client is its search. It covers all messages in your inbox and can also search within certain types of attached files (PDFs, Word docs, etc.).

On the collaboration front, it doesn’t have much beyond the ability to share folders (aka labels), calendars, and accounts.

Like Mailbird, eM Client offers basic AI drafting to help with typos and tone in replies.

On security and compliance, eM Client is GDPR compliant (though possibly outdated with 2018 references) and doesn’t have any external audits or certifications.

For pricing, eM Client has a sharp distinction between personal and business plans. There’s a free plan for non-commercial use, and paid plans are available as annual subscriptions or one-time payments.

The personal plan (without AI features) is $39.95/year or $49.95 one-time.

The business plan (with AI features) is $49.95/year or $188.95 one-time.

Both one-time payment options don’t include future feature updates. You can purchase lifetime upgrades separately at $90 per license.

If you’re looking for a slightly more productive version of Outlook and you want a free email app because you’re not using it for commercial purposes, eM Client might be a good option.

Apple Mail

If you’re a Mac user and you really don’t want to download another email client, does the default mail app from Apple work well for Outlook?

Well, compared to Thunderbird, Mailbird, and eM Client, Apple Mail isn’t going to give you any increased functionality.

If you use Apple Mail as your Outlook email client, you won’t have the integrated calendar or task management, and you’ll have to remember that folders are “labels” in Apple Mail.

The good news is that Apple Mail can support multiple accounts from multiple providers (via IMAP and SMTP standards), so if you have a Gmail account and an Outlook account that you’d like to unify into one well-designed, simple inbox, Apple Mail can do that.

If you want a free email client with a cleaner design than Outlook and don’t require advanced features, Apple Mail might be your best option.

Superhuman

When Superhuman first launched, it was solely focused on Gmail and Google email users. As of May 2022, it also supports Outlook users.

From a user interface perspective, Superhuman is the most distinct on this list. It looks nothing like an Outlook inbox, so if familiarity is a requirement, this might not be a good fit.

Superhuman offers several AI-powered features, the most notable being its ability to answer questions about your inbox.

Instead of traditional search (even as powerful as eM Client’s), you can ask your inbox direct questions. Instead of needing to remember a file’s name to look for a specific piece of information, you could ask: “What was the price that John from ACME quoted me?”

On the collaboration front, Superhuman offers the ability to @mention coworkers through Team Comments.

From a security and compliance perspective, it’s SOC 2 Type II, ISO 27001, CCPA, and GDPR compliant.

For pricing, Superhuman is on the higher end of this list, starting at $25/user/month on an annual plan.

Use cases and scenarios

To summarize our options for the best email client for Outlook users, we sorted them into two categories:

Individuals (you just want a better client for yourself)

• Thunderbird — you want open-source and lots of plug-in options
• Mailbird — you want Outlook, but with a unified inbox
• eM Client — you want robust search
• Apple Mail — you want a better design, with less functionality
• Superhuman — you want AI and shortcuts galore

Teams (you want an email client for coordination and collaboration within a team)

• Superhuman — you just want to be able to @mention instead of forward
• Missive — you want shared inboxes, internal @mentions, shared labels, canned responses, watch/assign… basically the best email client that’s collaboration-first

Hopefully this has been a helpful overview of the types of email clients out there for Outlook users. If you’re interested in Missive, continue on and we’ll get into some tactical information.

Recent heavy Outlook users who made the switch to Missive:

Stephanie at Lighting Dynamics, manages 100+ email quotes a day. Her team used to use Outlook for email management:

With traditional Outlook forwarding, once an email was out of the shared inbox, there was no visibility. We never knew if it had been handled. It was chaotic.

And now, with Missive: “Missive checked all our boxes. It was a huge relief to see we could maintain the shared inbox model — without building custom software from scratch.”

Or Kason, from i-SOLIDS, who grew his sales team beyond himself:

We got to a point where we weren’t providing the same level of communication, response, and service that allowed us to get to this point. We were relying on Outlook email and it was like ‘are you responding to that or am I?’

And after a month with Missive, Kason recommends: “Don’t think about just choosing a tool for today but this tool needs to work for scale too — that’s a major decision factor.”

How Missive integrates with Outlook

1. Create a free Missive account
2. Select your email provider (most likely Microsoft 365 or Outlook)

1. Determine how much history you’d like to sync (only paid accounts have unlimited history)

1. Repeat for as many different email accounts (shared or personal) as you need.
2. You have the option to sync contacts and calendar as well.

Get a detailed walk-through of how to configure Outlook to Missive, including terminology differences to help you get acclimated to your new inbox.

So what’s the best email client for Outlook users?

Like most things, it depends. If you’re a team that lives in their inbox day in and day out, and you’re looking for a collaboration-first inbox, give Missive a try.