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Dispatch by Mio

Slack vs Email — Talking to Your Customers

Slack vs Email

Slack vs Email. The age-old debate that has rolled on and on since, well since Slack launched.

Often touted the email killer, Slack has recently pivoted to labeling itself as the internal email replacement.

We know Slack is one of the most popular collaboration tools on the market for internal communications, but when it comes to external comms, we often resort back to email.

In this post, we look at why our behavior is what it is and learn if Slack vs Email will ever have an outright winner.

Table of Contents

  1. Intracompany Collaboration
  2. Intercompany Collaboration
  3. Slack vs Email: Pros and Cons
  4. Can Slack Replace Email?
  5. Alternatives to Email in the Workplace

When to use Slack vs Email?

Traditionally, there are two types of communication within a business:

  • Intercompany collaboration

Intracompany Collaboration

Intracompany collaboration is when you message your colleagues within the same company.

Your peers likely use the same Slack workspace and all your employees have a Slack account.

In the left-hand pane of your Slack workspace, you have a list of channels and the option to start or continue a direct message (DM) with anyone in your company.

This can be both one-to-one messages or group messages.

You can see below, I regularly message Jennifer one a one-to-one basis. Further down, you will see I often message Meredith and Tom together in a group message.

Direct messages in Slack

When your entire organization (or the people you regularly message) use Slack in the same workspace, the need for one-to-one and group emails becomes near redundant.

Everything you need to say via email can be communicated within a Slack DM.

For internal project work, Slack introduced channels to the world of collaboration.

As you see below, every topic of group conversations I have is contained within the Channels section.

Channels in Slack

This removes the need for me to ever send a “group email” and means everybody can respond in one place, with the ability to neatly organize responses via threads.

So, if everyone inside your organization uses Slack to chat, Slack’s ambition to be the internal email replacement is almost complete.

If everyone isn’t on Slack, Mio’s interoperability product helps connect Slack to other platforms like Microsoft Teams and Cisco Webex Teams. Click here to see Mio’s interoperability in action.

Intercompany Collaboration

Intercompany collaboration is when people within different organizations need to collaborate with each other.

When everybody inside your company uses Slack, collaboration and communication are simple.

However, the amount of work we engage external parties in has increased exponentially…


  • That’s a rise of 3.7 million since 2014.
  • Add to that the number of employees with side gigs and you’ve got a whole lot of external collaboration on your hands.


  • Working with customers to finalize proposals, prepare adoption plans, or check-in post-implementation has become easier with technology.
  • Naturally, a digital communication line is preferred to constant travel and meetings.


  • Common practice has changed from creating a Slack channel to talk about a partner to creating a shared channel where the partner has access to documents, decisions, and conversation.


  • A common interface and collaboration hub has proven to be the preference instead of working in silos.

Given the increasing number of external contributors to businesses, it’s frequently the case that other businesses are using apps other than Slack.

Microsoft Teams, for example, now boasts 20 million users.

While we know that 66% of companies using Microsoft Teams are also using Slack, this still leaves 6.8 million users that are using a different platform to you.

When this is the case, we often resort to email, a mutually agreed third party tool for a video conference, or an in-person meeting.

The best solution for intercompany collaboration

Mio has created universal channels for Slack with Microsoft Teams or Webex Teams…

Stay in Slack and chat with Microsoft Teams users and Webex Teams users

You can stay in Slack and send messages to your contractors, suppliers, or clients that use Microsoft Teams or Webex.

They stay in their platform too and Mio translates the messages across platform.

And it’s not just messages that are supported! GIFs, emojis, channels, DMs, and message edits/deletes are all supported.

If this sounds like something you need, click to install your first universal channel here.

Slack vs Email: Pros and Cons

When searching for advantages over Slack over email, you could find yourself in a list of features that probably doesn’t mean a lot unless you’re already using Slack.

Google also tells us there are over 7 million results for this query so let me save you the time.

Advantages of Slack vs Email

Slack Pros vs Email

I’ve rounded up the most popular suggestions for advantages of Slack vs email…

  1. There’s no chance of accidentally deleting an important email — Slack is persistent chat and the entire thread of conversation remains available.
  2. Channels provide areas for your conversation topics to be broken down into — save you searching for that specific email at the last minute.
  3. Rapid communications enable the ability to come together as a team and brainstorm anywhere and at any time.
  4. While email integrations exist, the number of Slack integrations now far exceeds the amount you can integrate with email.

You may also like: Top 37 Best Slack Integrations, Apps, and Bots for 2020

These are only the most commonly suggested advantages of Slack over email.

Slack customization

As you start to use Slack, you can customize your workspace to the way you work.

If you chat with someone constantly, you might want to “star” the conversation so it appears at the top of your Slack workspace.

See below where I have starred a channel, a multi-party conversation, and two direct messages that are either my most used or most important. Starring a message moves these to the top of your channels and messages.

Starred messages in Slack

Slack as a hub for work

The most distinguishing advantage of Slack over email is that everything (okay almost everything) is — or can be — in one UI.

When your work hub is your email client, you forever switch between your chat tool, your telephone, and your meetings platform.

With Slack, all your messages are in the same UI and have quick access to a whole host of communication and collaboration features are literally at your fingertips.

Outside of the functionality that Slack provides, there are some more strategic advantages that Slack provides over email…

Slack as the expected tool of choice

Attracting talent in 2020 is different to attracting talent when email was revolutionary.

If you want to hire the best staff, you need to provide the tools they want to use.

For example, hiring a marketing professional that thrives with productivity tools would be counterintuitive if you force them to use email to collaborate with colleagues and contractors.

According to the Office Hours blog, Slack is best when:

  • If you want to share & collaborate on something in real-time
  • If you need an immediate response

Only yesterday, I was sat in a coffee shop working with a friend that works at another company who was criticized for not responding to an email quickly enough.

Email is not the appropriate tool here.

Slack Cons vs Email

In certain scenarios, the cons of Slack vs Email rear their head. Let’s address those here.

Everybody is let loose to do their own thing

Without appropriate guidelines, Slack users could be subject to notification overload.

For example, it is common practice to start a thread when replying to someone’s post in a channel. This way you don’t interrupt everyone in the channel — and it’s obvious you are still referring to the topic outlined in the initial post.

Below you can see where Rebekah asked about a specific article she was helping with and we discussed in the thread as replies.

I then start another conversation in this channel about the plan for next week so nobody could get the context of the conversation confused.

Threaded messages in Slack

Not everyone is on Slack

The most obvious con of using Slack as an email replacement is that not everyone uses Slack.

When people outside your organization use other team collaboration platforms — like Microsoft Teams or Cisco Webex Teams — staying in Slack feels impossible.

But that’s where Mio comes in.

When you want to use Slack, but your clients prefer Microsoft Teams or Webex Teams, save yourself from dropping what you are doing and moving over to another platform.

Mio enables you to stay in Slack and chat to your customers as if they were on Slack.

The best part? They stay in their chat app too.

Mio translates the messages from one platform to the other so you don’t need to resort to email or set up a conference call.

If you want to stay in Slack, instead of resorting to email when talking to your customers, try Mio free here.

Can Slack Replace Email?

Slack has changed its own branding from email killer to internal email replacement.

Slack itself requires an email address to first sign into a Slack workspace. So killing email would require Slack to replace the entire “login with email” element of their own tool.

Such a change would cause an unthinkable amount of change in the way people login to apps, websites, and even hardware that the email address will seemingly never die.

However, replacing the practice of sending an email isn’t impossible.

But it is still a long way away.

When I spoke to Robert Vis, CEO of MessageBird in early 2019, he told me:

“The legacy that email will have is huge and the reality is that email is sometimes efficient. Maybe in a millennial world, everybody is texting five, six, seven words. But, we need to cater for all personas and email is still high on the list for a lot of people.”

Little has changed in a year. The people inside and outside your business that prefer email still prefer email.

The barrier to replacing the process of sending an email could be replaced by team collaboration apps — rather than just by Slack.

I am on the side of team collaboration. For me, email is clunky. I celebrate a small volume of emails when I wake up and check my phone.

If your customers are using other apps like Microsoft Teams, convincing them to move to Slack so they can chat with you is unlikely.

The compromise can only be one of two things:

  1. Allow your customers to use their team collaboration platform of choice and connect to them through a federation service like Mio

You may also like: 6 Ways to Connect Slack and Microsoft Teams

Alternatives to Email in the Workplace

I reached out to my network to see what everyone else was using, other than Slack or email, for external collaboration.

I asked: What Happens When You Need To Chat Externally?

Sunny Dhami, RingCentral

Sunny Dhami, Director of Product Marketing at RingCentral, said it’s about how you manage this as a business.

“Some collaboration tools do give you the ability to add guests and collaborate with them within the tool but it’s all dependant on how the business wants to engage with external contacts. I use a mix of both, depending on the outcome I’d like to achieve.”

Tom Arbuthnot, Modality Systems weighs in on Slack vs Email

Tom Arbuthnot, Principal Solutions Architect at Modality Systems, said it depends on the external party’s culture and who has the “power” in the relationship.

“In our case, if a customer is on the same platform or has access, that’s great. If not, email is the common denominator. Using email ‘sometimes’ doesn’t mean no use case for team chat.”

Karoliina Kettukari, Sulava

Karoliina Kettukari, Senior Consultant at Sulava, mentioned her experience in Microsoft Teams — seemingly Slack’s largest competitor.

“If it’s a project, we have a common workspace with other parties. If it’s a limited number of single messages we need to exchange then e-mail and phone will do. Depending on federation policies, Teams chat may work too.”

April Diehl, Spectrum Enterprise

April Diehl, Network Engineer at Spectrum Enterprise mentioned how useful Skype for Business federation was when collaborating externally.

“In many cases I use Skype for Business with customers who also have Skype open to external contacts. I have used Slack in the past with customers and it is great because it tracks the conversation and you can upload documents to it as needed. Email works but keeping track of the conversation if there are multiple threads is cumbersome.”


Email is unlikely to disappear any time soon.

That doesn’t mean you must remain totally loyal to it. And, in most cases, you are doing your team collaboration tools a disservice.

The reality is that most of your contacts probably have a team collaboration tool.

If they use Slack too, Slack’s shared channels feature is perfect for this.

If they don’t use Slack, it’s not the end of the world.

Email will always be there. But the more productive method is for you to stay in Slack and your customers to stay right where they are.

Final Words

Do you communicate with people outside your organization?

Do they use apps other than Slack?

If the answer is yes to both of these questions, according to research, they’ll likely be using Microsoft Teams or Cisco Webex Teams.

When this is the case, you don’t have to resort to email.

Mio has created universal channels for Slack with Microsoft Teams or Webex Teams…

You can stay in Slack, leave email well alone, and send messages to your contractors, suppliers, or clients that use Microsoft Teams or Webex.

They stay in their platform too and Mio translates the messages across platform.

And it’s not just messages that are supported! GIFs, emojis, channels, DMs, and message edits/deletes are all supported.

If this sounds like something you need, try Mio for free here.

Read Next: Ultimate Guide to External Federation in Slack, Microsoft Teams, & Webex Teams



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Chat better, together. Mio powers cross-platform messaging across Microsoft Teams, Slack, Webex, and Zoom. Learn more at https://m.io