Mailboxes are the mail addresses that can receive and send mail. Per mailbox: one login, one password, one storage area. You create them as domain admin in the Mailcow GUI; depending on your plan you have a certain quota of them.
Creating a new mailbox
In the Mailcow GUI:
- Configuration → Mailboxes.
- Click Add mailbox at the top right.
In the dialog:
| Field | Value |
|---|---|
| Email address | local part (before the @), e.g. info |
| Domain | from the dropdown — your domain(s) |
| Full name | display name, e.g. “Sports club board” |
| Password / repeat password | initial password for the user |
| Quota | storage size in MB (e.g. 2048 for 2 GB) |
Optional:
- Force password update at first login: handy when you send the password to someone else — they have to change it at first login.
- Force SOGo webmail access: allows SOGo only, no IMAP/SMTP for external clients.
Click Add. The mailbox is active immediately — mails land in it from now on, the user can log in to SOGo or set up a mail client.
Understanding quota
Quota is the upper limit of how much storage this mailbox may occupy. When the limit is reached, the server rejects incoming mails and the sender gets a bounce.
Recommendations from our experience:
- Private mailbox, normal use: 2–5 GB
- Business mailbox with lots of attachments: 10–20 GB
- Newsletter-receiving mailbox: 1 GB is often enough if the user deletes regularly
- Role mailbox (info@, kontakt@): 5 GB to be safe
You can adjust the quota anytime afterwards — open the mailbox entry → change quota → save. Effective immediately.
Important: the sum of all quotas must not exceed the limit of your mail server plan. The dashboard shows how much you have left.
Editing a mailbox
Click an address in the mailbox list → Edit.
What you can change:
- Active / inactive: lock the mailbox without deleting it — mails are rejected, but the data stays.
- Full name
- Quota
- Password: assign a new password — the user will have to sign in with the new one at the next login.
- Enforce TLS: mails to this mailbox are only accepted over encrypted connections. We recommend leaving this on.
- Sender restrictions: which addresses may send with this mailbox (default: only its own address).
Save → changes are live immediately.
Changing passwords
Three ways:
- As domain admin for a user mailbox: edit the mailbox → assign a new password.
- As the user themselves: via SOGo webmail or the Mailcow user login page.
- Via API: for script automation. Open a ticket, we set up API access for you if you want to use it.
For security reasons we recommend: users change their passwords themselves, you as domain admin only set the initial password.
Deleting a mailbox
Select the mailbox → Delete. Confirm.
Careful: the data is gone immediately. If the user still needed anything from the mailbox, it’s lost. Before you delete:
- The user exports their mails (in SOGo: select all mails → export as
.eml, or as an IMAP sync to another account). - Or: you set the mailbox to “inactive” first, wait 30 days, then delete.
Mail forwarding and out-of-office
These features live NOT in the mailbox area, but in SOGo webmail:
- Forwarding: SOGo → Settings → Filters — create a rule with “forward everything to X”.
- Vacation notice: SOGo → Settings → Vacation — text, dates, automatic reply.
More in Personal Sieve filters in webmail.
Best practices
Assign role addresses instead of personal addresses. vertrieb@deinverein.de and it@deinverein.de outlive claudia@deinverein.de — when Claudia leaves, you don’t have to rename the address on every external business card. Set up personal addresses as additional aliases.
One mailbox per user, no shared logins. If three people access info@deinverein.de with the same password, nobody knows who answered what. Better: one mailbox per person (vorname@), and a shared info@ as a shared folder via SOGo sharing or as an alias.
Leave “enforce TLS” on. Mails without TLS do travel the internet, but only when the receiving side actively supports TLS anyway. Practically all mail servers do these days. Turning TLS off gains you nothing — it just permits unencrypted transfer.
Don’t set quotas too tight. When a mailbox runs against its quota limit, the user stops receiving mail — that’s the classic source of “we sent you something, but it never arrived”.
Frequently asked questions
How many mailboxes can I create? Depends on the plan. Solo and Pro: 1 mailbox. Family: 5. Team: 25. Club: 100. Business: unlimited. The dashboard shows your limit; the plan details are on the Mailhosting product page.
What’s the difference between a mailbox and an alias? A mailbox has its own storage and login. An alias is just a forwarding rule — mails to the alias land in the target mailbox. More in Aliases and catchall.
Can one user have multiple mailboxes? Technically yes — each mailbox has its own login. In practice it’s often more sensible to have one main address and additional addresses as aliases.
What happens when the domain quota is full and I want to create another mailbox? Mailcow rejects the creation. Solution: reduce existing mailbox quotas or upgrade your mail server plan.
Is storage specified in MB or GB? In MB. 1024 MB = 1 GB. From our own experience: at first, people like to assign 50 MB quotas, then mails bounce — better 2000 MB (2 GB) as the default, then you have peace.
What if a user forgot their password? You as domain admin change the password. SOGo has no “forgot password” self-service flow by default.
Does IMAP work immediately after creating a mailbox? Yes. As soon as the mailbox exists in Mailcow, the user can set it up via IMAP/SMTP right away — calendar and contacts come via CalDAV/CardDAV (SOGo) on top.
Can I import mailboxes? Yes, for migrations. The fastest way: the free self-service migration tool in the mailbox backend — enter the old provider’s credentials, the sync runs in the background. If we should handle the complete migration: open a ticket, we do that for a flat fee — conditions on the Mailhosting product page.
What’s next
First login as domain admin in the Mailcow GUI
After ordering your mail server plan, you get access to the Mailcow GUI. Here's an overview of what you see as domain admin and where to find what.
Setting up aliases and a catchall
Route several mail addresses into one mailbox — info@, kontakt@, presse@ all in a single inbox. Plus a catchall for every typo address.
Creating app passwords for mail clients
With 2FA active, Outlook, Apple Mail and friends need an app password instead of your main password. How to create them, revoke them and avoid password chaos.
Setting domain-wide Sieve filters as domain admin
Filters that apply to all mailboxes of your domain at once — for example to sort newsletters domain-wide into a specific folder or to reject certain senders.