Maximum number of email users recomended with proper hardware

HI There,

I am evaluating Mail-in-a-box for several use cases in SMB market like 150 to 500 mailboxes for companies in the business to business market.
Also I have a client, a small university that need 6000 mail boxes.

I normally deploy in AWS but can do it on a data center but always on virtual environment, so I can assign computer, memory and storage as needed.

My question #1 is: How big Mail-in-a-box can be in terms of quantity of mailboxes. Can support heavy load?
Question #2: Can I set up a cluster or any highly available servers farm?
Question #3: Can I get eventual or permanent support service,
Question #4: Is there any version that uses MySQL or PostgreSQL for big deployments?

If I deploy this software I plan to contribute ($$) for any commercial deployment I have.

Pleases advice


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Whilst the components used within MiaB can certainly handle most of what you propose, your use is beyond the scope of this project.

MIAB is best for SMB usage, I find… we have it deployed with about 100 mailboxes, of which about 20 see heavy usage, on a 1GB RAM, 1 vcpu, with no performance issues at all. We scale up storage as required.

6000 mailboxes - in theory it would work, but in practice, this may not be the best application, as alento mentioned.

Thanks Alento for the information.


This is the information I was looking for I figured that for SMB with about 200 users MIAB would be fine.

I appreciate your help.

The amount of 6000 mailboxes is probably not a problem if the I/O of your hardware is sufficient. That will be the first bottleneck; probably a little bit more memory then 1 GB is also nice, due to the high amount of concurrent connections.

You will, however, run into problems with the provided web-interface. That is build - as stated above - for SMB usage.

Keep also in mind that having 6000 users, some of them will have a virus, can’t receive messages etc. So you have to provide some support.

If you need a solution like this, i should separate NextCloud and the mailplatform and configure it myself. Also should i look to a better thing for maintaining accounts. MiAB could be used as a guide.

Thanks sander-schippers for your answer.

I probably won’t consider MIAB for 6K mailboxes from start but it is good to know that it may work providing the proper infrastructure resources. Now I know if any of my clients get 1K mailboxes it would be fine.

I am curious about your last comment regarding changing the deployment architecture. I see that MIAB also deploy nextCloud for Contacts and Calendar. In fact I use nextCloud running on Linux.

In some of my use cases, nextCloud would be preexisting to MIAB deployment so I would like to deploy MIAB only and integrate with the already running nextCloud.

Is there any documentation or post you would suggest me for editing the setup script and modify the deployment architecture?
I was taking a look at the git hub repo and see that I should start at I am not afraid of that but if there is a quick reference that helps me expedite the process, would be better.


Virus?? May I know how do we resolve it and how do we detect virus?

I thought we are on ubuntu so we would not have this problem.

Please note that @sander-schippers is referring to the users themselves, not the Mail-in-a-Box.