Security First Infrastructure

Mailcow Mailserver

This FAQ answers the most common questions customers have before, during, and after renting a Mailcow mailserver.

⚠ Important: Acceptable Use Policy – No Spam Tolerated!

Spamming, bulk unsolicited email, and any form of email abuse are strictly prohibited on our mailservers.

This is not just a formality. Sending spam has serious consequences that affect everyone:

What counts as spam / prohibited use:

Consequences of violation:

By using our service, you agree to these terms. If you have any doubt about whether a planned mailing is acceptable, please contact us first – we are happy to advise and, if needed, help you set up a proper transactional email service.

Table of Contents

1. General Questions

What is Mailcow?
Mailcow is a complete, open-source mailserver suite that runs inside Docker containers. It includes everything you need for professional email: SMTP (Postfix), IMAP/POP3 (Dovecot), anti-spam (Rspamd), webmail (SOGo), ActiveSync for mobile devices, calendars, contacts, and a modern admin interface.
Why choose a self-hosted mailserver over Gmail or Microsoft 365?
  • Data ownership – your mail stays on your server, under your control.
  • Privacy – no third party scans your emails for advertising or AI training.
  • Predictable cost – flat monthly fee instead of per-user licensing.
  • Unlimited aliases and domains – add as many as you want at no extra cost.
  • Compliance – easier to meet GDPR and data-residency requirements.
What are the downsides of running your own mailserver?
  • Requires proper DNS configuration (SPF, DKIM, DMARC, PTR).
  • Deliverability depends on IP reputation – a new IP may initially end up in spam folders.
  • If the server goes offline, mail is queued but delivery is delayed.
  • Needs regular updates and monitoring (usually included in managed plans).
Is Mailcow suitable for business use?
Yes. Mailcow is used by thousands of small and medium-sized businesses. It provides the same core features as Microsoft Exchange or Google Workspace: shared calendars, contact sync, mobile push (ActiveSync), spam filtering, and a webmail interface.

2. Setup & Onboarding

How long does setup take?
A basic setup usually takes 1–2 business days after we receive your completed questionnaire and DNS access. More complex migrations (many mailboxes, custom configurations) may take up to a week.
What do I need to provide to get started?
  • A domain name (or permission to register one for you).
  • Access to DNS management (or we can handle DNS for you).
  • List of mailboxes, aliases, and distribution lists.
  • If migrating: access credentials for the old mail system.
Can I try it before committing?
Yes, we offer a trial period on a temporary subdomain so you can test the webmail, create mailboxes, and send/receive mail before switching your production domain.

3. Domains & DNS

Do I need my own domain name?
Yes. To send and receive email at you@yourcompany.com, you need to own yourcompany.com. If you don't have one yet, we can help you register one.
Can I use multiple domains on one mailserver?
Absolutely. Mailcow supports unlimited domains on a single server. You can have sales@company-a.com and info@company-b.com delivered to the same or different mailboxes.
What DNS records need to be set?
Record Purpose
MX Tells the world which server receives mail for your domain.
A / AAAA Points the mailserver hostname to an IP address.
SPF Authorizes the server to send mail on behalf of your domain.
DKIM Cryptographically signs outgoing mail to prove authenticity.
DMARC Tells receiving servers what to do if SPF or DKIM fails.
PTR Reverse DNS – critical for deliverability. Set at your hosting provider.
Autodiscover / Autoconfig Helps mail clients configure themselves automatically.
Can you manage DNS for me?
Yes. If you give us access to your DNS provider (or delegate the zone to us), we will set up all required records and maintain them. Alternatively, we provide a list of records for you to add yourself.
What happens if I move my domain elsewhere later?
Your data and configuration remain yours. We'll help you export mailboxes (IMAP or archive) and you can point DNS to a new provider whenever you choose. No lock-in.

4. Mailboxes & Users

What's the difference between a mailbox, an alias, and a forwarder?
  • Mailbox – a real account with a password, storage, and login (e.g. john@example.com).
  • Alias – an additional address that delivers to an existing mailbox (e.g. info@ → john@). No extra login, no extra storage.
  • Forwarder – sends mail to an external address (e.g. forward everything to a Gmail account).
How many mailboxes can I have?
There is no hard limit in Mailcow itself. The practical limit depends on your server's CPU, RAM, and storage. Our plans typically include a set number of mailboxes, with the option to add more.
Can I have shared mailboxes (like "support@" that multiple people access)?
Yes. You can create a mailbox and grant multiple users ACL access (shared folder access) so a whole team can read and reply from the same mailbox.
Can I set up a catch-all address?
Yes. A catch-all forwards any mail sent to a non-existent address at your domain to a specific mailbox. Useful for catching typos, but can attract spam – use with care.

5. Migration

Can I migrate mail from Gmail, Outlook, or another provider?
Yes. Mailcow includes an IMAP sync tool that pulls existing mail from virtually any provider (Gmail, Outlook/Microsoft 365, cPanel, Exchange, etc.). We handle this as part of the onboarding if requested.
Will my folders and labels be preserved?
Folders are preserved. Gmail labels are converted to folders (since a message with multiple labels would otherwise appear multiple times, we configure filters to avoid duplicates).
Will there be downtime during migration?
No. We do an initial sync while your old mail is still active, then switch the MX records at a planned moment. A final sync catches any mail that arrived during the DNS switch. Users typically notice no interruption.
Are contacts and calendars migrated too?
Email itself is migrated automatically. Contacts and calendars need to be exported from the old provider (e.g. as .vcf and .ics files) and imported into SOGo. We can assist with this.
How long does migration take?
Depends on mailbox size and the old provider's speed. A 1 GB mailbox can take 30 minutes to several hours. Gmail in particular throttles IMAP, so very large accounts may take a day or more.

6. Email Clients & Webmail

Which mail clients are supported?
All standard clients: Outlook, Thunderbird, Apple Mail, Gmail app, Samsung Mail, iOS Mail, and any IMAP/SMTP-compatible client. For mobile devices, ActiveSync provides push mail, contacts, and calendar sync.
Is there a webmail interface?
Yes. Mailcow includes SOGo (with calendars, contacts, and task management) and optionally Roundcube (lightweight, mail-only). Accessible from any browser at https://mail.yourdomain.com.
Can I use it on my phone?
Yes. We provide setup instructions for iOS and Android using either IMAP or ActiveSync. ActiveSync is recommended because it supports push notifications and syncs calendars/contacts automatically.
Does it support shared calendars and contacts?
Yes. SOGo supports CalDAV and CardDAV. You can share calendars and address books between users or publish them publicly.

7. Security & Privacy

Is my mail encrypted?
In transit: yes – all connections (SMTP, IMAP, webmail) use TLS encryption.

At rest: mail is stored on an encrypted disk (if enabled on your plan), but it's not end-to-end encrypted by default. For E2E encryption, users can use PGP or S/MIME in their mail client.
Does the server support two-factor authentication (2FA)?
Yes. Both admin and user accounts can enable 2FA via TOTP (Google Authenticator, Authy, etc.) or YubiKey.
Who can read my email?
On a self-hosted or managed Mailcow instance, only you (and our administrators if you use managed hosting) have access. We do not read, scan, or analyze your mail content. You can request full-disk encryption for additional protection.
Is my data GDPR-compliant?
Yes. We can host your server in the EU, sign a Data Processing Agreement (DPA), and implement retention and deletion policies according to your compliance needs.
What happens if there's a data breach?
We follow a documented incident-response procedure: immediate isolation, investigation, customer notification within 72 hours (as required by GDPR), and remediation. Regular security audits and updates minimize the risk.

8. Deliverability & Spam

Will my emails land in spam folders?
Not if DNS is configured correctly. We set up SPF, DKIM, DMARC, and PTR records – the same mechanisms Google and Microsoft require. New IPs sometimes need a short "warm-up" period, but within a few days, deliverability stabilizes.
What is IP reputation and why does it matter?
Receiving mailservers track the sending history of each IP address. A clean IP that sends normal traffic earns a good reputation and is trusted. A shared or abused IP may be blacklisted. We use dedicated IPs with clean history for our mailservers.

⚠ This is why we have a strict no-spam policy: a single customer sending spam can ruin the reputation of the IP for every other customer on the same infrastructure. See the Acceptable Use Policy for details.
How does Mailcow filter incoming spam?
Mailcow uses Rspamd, a modern spam filter with:
  • Bayesian learning (adapts to your mail patterns).
  • DNS blacklist checks.
  • SPF/DKIM/DMARC validation.
  • Greylisting for first-time senders.
  • Custom allow/block lists per domain or mailbox.
What if a legitimate email is marked as spam?
Users can mark mails as "not spam" in webmail – Rspamd learns from these actions. You can also add specific senders or domains to an allow-list.
Can I send newsletters or bulk mail from this server?
⚠ No – our mailservers are for regular business correspondence only. Sending newsletters, marketing blasts, or any form of bulk mail from our servers is not allowed, even to recipients who have opted in.

Reasons:
  • Bulk sending triggers blacklists and damages the IP reputation for all customers.
  • Our upstream hosting provider may treat it as abuse and suspend our services.
  • Deliverability of your regular business mail would suffer.
For newsletters and marketing campaigns, use a dedicated transactional email service such as:
  • Mailgun
  • SendGrid
  • Amazon SES
  • Postmark
  • Brevo (Sendinblue)
  • Mailchimp
These services are designed for bulk mail, handle bounces and unsubscribes correctly, and protect your domain's reputation. We're happy to help you set one up.

9. Storage & Quotas

How much storage do I get per mailbox?
Depends on your plan. Quotas are flexible – you can assign, say, 10 GB to a power user and 2 GB to a general account. Total storage is pooled at the server level.
What happens when a mailbox is full?
New mail is rejected with a "quota exceeded" message to the sender, and the user is notified. Admins can increase the quota at any time via the Mailcow UI.
Can I upgrade storage later?
Yes. Storage can be expanded at any time without downtime. Contact us to upgrade your plan.

10. Backup & Retention

Is my data backed up?
Yes. Managed plans include automated daily backups with configurable retention (typically 30 days). Backups are stored off-site and encrypted.
Can I restore a deleted email?
Yes, in multiple ways:
  • From Trash – users can restore within the trash retention period (default 30–90 days).
  • From backup – administrators can restore individual mailboxes or specific dates on request.
  • From archive – if compliance archiving is enabled, every mail is preserved in a hidden archive mailbox.
How long are deleted emails kept?
Configurable per mailbox:
  • Trash folder: default 30 days, extendable to "forever".
  • Backups: default 30 days of daily snapshots.
  • Compliance archive (optional): indefinite.
Can I export my mailboxes?
Yes. You own your data. You can download mailboxes via IMAP at any time, or request an export in .mbox or .eml format.

11. Billing & Contracts

How is the service billed?
Flat monthly or yearly fee depending on the plan. No per-mailbox licensing. Yearly plans typically include a discount.
Is there a minimum contract period?
Standard plans run month-to-month with no minimum term. Longer commitments (1 year, 3 years) are available at reduced rates.
What happens if I cancel?
We export your data in a portable format (IMAP-compatible) and give you time to transition. After the cancellation date, the server and all data are securely wiped.
Are there setup fees?
A one-time onboarding fee may apply for complex migrations or custom configurations. Standard setup with a new domain is included in the plan.

12. Support & Maintenance

Who maintains the server?
On managed plans, we handle all maintenance: security updates, Mailcow upgrades, monitoring, backups, and SSL renewal. On self-managed plans, you handle these yourself (we can still provide guidance).
When are updates applied?
During a pre-agreed maintenance window (typically outside business hours). Updates are tested first and usually cause no noticeable interruption.
How do I contact support?
Support is available via email, phone, or ticket system depending on your plan. Response times range from 4 hours (business plans) to next-business-day (basic plans).
What is the uptime guarantee?
We target 99.9% uptime (roughly 45 minutes downtime per month). Scheduled maintenance is announced in advance and typically causes no downtime due to graceful updates.
What if the server goes down?
Incoming mail from other servers is queued by the sender for up to several days and delivered when the server comes back. No mail is lost. Our monitoring alerts us immediately, usually before customers notice.

13. Troubleshooting

I can't send email – what do I do?
Common causes:
  • Wrong password – try logging into webmail to verify.
  • Blocked port 25/587 – some home ISPs block outgoing SMTP. Use port 587 with authentication.
  • Firewall or VPN – temporarily disable to test.
  • Rate limit triggered – if you've sent a large volume recently, you may have hit the anti-spam rate limit. Contact support.
If none of these help, contact support with the exact error message.
I'm not receiving emails – what's wrong?
Check:
  • Spam/Junk folder in webmail.
  • Mailbox quota – is it full?
  • Any filters/rules that may be moving or deleting mail.
  • DNS MX records point to the correct server.
If the issue persists, we can check server logs for the missing message.
My emails go to recipients' spam folders – why?
Usually one of:
  • Missing or wrong SPF / DKIM / DMARC records.
  • Missing PTR (reverse DNS) record.
  • IP reputation still warming up (usually resolves in a few days).
  • Content triggers spam filters (too many links, all caps, attachments).
We can run a diagnostic using tools like mail-tester.com to pinpoint the issue.
Outlook keeps asking for my password – how do I fix it?
Usually caused by:
  • A recent password change – update it in Outlook.
  • Outlook's credential cache – clear stored passwords in Windows Credential Manager.
  • 2FA enabled – you need an app-specific password instead of your regular one.
How do I change my password?
Log into webmail at https://mail.yourdomain.com and go to Preferences → Password. Or ask your administrator to reset it.

14. Acceptable Use Policy (AUP)

⚠ What is not allowed on our mailservers?
The following activities are strictly prohibited and will result in immediate suspension:
  • Unsolicited bulk email (spam) – sending messages to recipients who did not explicitly opt in.
  • Purchased, scraped, rented, or harvested mailing lists – even if you think the recipients might be interested.
  • Phishing, scams, or fraud – impersonating others, fake invoices, "Nigerian prince" schemes, etc.
  • Malware distribution – sending viruses, trojans, ransomware, or malicious links.
  • Marketing campaigns – bulk promotional email (even to opted-in subscribers) must go through a dedicated service, not our servers.
  • Forged sender identities – pretending to send from a domain you don't own.
  • Harassment or illegal content – threats, hate speech, child sexual abuse material, or anything unlawful in our jurisdiction.
  • Open relays – allowing third parties to send mail through your mailbox.
Why is spam such a big deal?
Email spam has cascading consequences:
  1. Blacklists – IPs that send spam get listed on services like Spamhaus, Barracuda, and SORBS. Once listed, even legitimate mail gets rejected.
  2. Shared reputation – if our IP range is blacklisted, every customer on our infrastructure suffers, not just the offender.
  3. Hosting provider action – our upstream provider (the datacenter / cloud provider) monitors abuse complaints. Repeated incidents can result in our entire infrastructure being suspended.
  4. Recovery is slow – removing a domain or IP from a major blacklist can take days or weeks, and some blacklists don't remove entries at all.
  5. Legal exposure – spam violates laws like GDPR (EU), CAN-SPAM (US), CASL (Canada), and others, exposing both the sender and us to fines.
What happens if I (or one of my users) sends spam?
Our response escalates based on severity:
  1. First incident (small scale, likely accidental): immediate rate-limiting, warning, and cleanup assistance.
  2. Confirmed abuse or repeated incidents: suspension of the offending mailbox or domain.
  3. Serious or deliberate abuse: termination of the service contract without refund.
  4. Damages caused: the customer is liable for blacklist removal fees, loss of service to other customers, and any other damages.
We will always try to contact you first if we suspect a compromised account rather than malicious intent – but we must act quickly to protect other customers.
My account sent spam but I didn't do it – what happened?
This usually means your mailbox or a device has been compromised. Common causes:
  • Weak or reused password that was leaked in another breach.
  • Malware on a computer or phone that stole credentials.
  • Phishing attack that tricked you into entering your password on a fake page.
Immediate actions:
  1. Change the mailbox password immediately.
  2. Enable two-factor authentication (2FA).
  3. Scan your devices for malware.
  4. Review recent sent mail and login history.
  5. Contact us – we can help investigate and unlock the account.
I want to send a legitimate announcement to my customers – is that OK?
Small, occasional, personal communications are fine (e.g. a few dozen notifications to existing clients). But if you're sending:
  • The same message to more than ~50 recipients, or
  • On a regular/scheduled basis (newsletters), or
  • To a list you maintain for marketing purposes,
…please use a proper transactional service (Mailgun, SendGrid, Brevo, Mailchimp, etc.). When in doubt, contact us first. We'd much rather help you set things up correctly than deal with a blacklist afterwards.
Still have questions? We're happy to help. Contact us via the details in your service agreement.