Mailcow VPS Hosting: RAM, Storage and Real Cost

For production Mailcow VPS hosting, use a KVM virtual machine with at least 8 GB RAM and enough disk for the operating system, Mailcow services, live mail, indexes, quarantine, and growth. Mailcow does not support LXC or OpenVZ. Its official minimum is 6 GiB RAM plus 1 GiB swap, while 8 GiB is recommended for approximately 5 to 10 users. Among the current standard ServerSpan plans, vm.Go is the first comfortable match: 8 CPU cores, 16 GB RAM, and 250 GB SSD for €32.99 per month excluding VAT.

Written by the ServerSpan Technical Team

Mailcow requires KVM rather than a container VPS

Mailcow is distributed as a Docker Compose stack, but that does not mean it should run inside any product sold as a VPS. The official Mailcow system requirements explicitly exclude OpenVZ, Virtuozzo, LXC, and similar container platforms. KVM and other full virtual machines are supported.

This immediately removes the lower-cost ServerSpan container plans from the comparison. Even ct.Go provides 8 GB RAM, but it is still an LXC-based service and therefore is not a supported Mailcow target.

Choose from the KVM range or request a custom KVM allocation. The distinction matters because Mailcow controls a substantial Docker networking and service stack. Installing it on an unsupported virtualization layer may appear to work initially, then fail around networking, firewall handling, kernel behaviour, or upgrades.

The ServerSpan guide comparing KVM VPS and container VPS explains why applications that manage Docker and networking directly belong on a full virtual machine.

The official minimum is not a sensible purchasing target

Mailcow requires at least 6 GiB RAM plus 1 GiB swap in its default configuration and 20 GiB of disk before any messages are stored. The same documentation recommends 8 GiB RAM for approximately 5 to 10 users.

Mailcow is larger than a basic Postfix and Dovecot installation. Its default stack includes SOGo, MariaDB, Redis, Rspamd, ClamAV, full-text search, Nginx, Postfix, Dovecot, Unbound, certificate handling, and supporting web services.

Mailcow notes that one SOGo worker can use roughly 350 MiB before it is purged and that the default configuration starts 20 workers. It gives 16 GiB RAM as a planning example for 15 phones using ActiveSync and about 50 concurrent IMAP connections.

You can disable ClamAV or the full-text search engine to reduce memory use. That is a feature tradeoff, not a good reason to force a business mail server onto an undersized VPS. Disabling antivirus changes how attachments are inspected. Disabling full-text indexing changes mailbox-search behaviour.

The current KVM plans produce one clear default choice

ServerSpan plan	Resources	Mailcow requirement match	Current monthly cost	Verdict
vm.Ready	2 cores, 2 GB RAM, 25 GB SSD	Far below the official RAM minimum; disk leaves almost no space for mail	€9.99 excluding VAT	Reject for Mailcow
vm.Steady	4 cores, 4 GB RAM, 100 GB SSD	Useful disk allocation, but RAM remains below the official minimum	€17.99 excluding VAT	Do not deploy Mailcow on the standard configuration
Custom KVM with 8 GB RAM	Resource allocation to be confirmed	Matches the official recommendation for approximately 5 to 10 users	Needs human verification	Reasonable small-installation target
vm.Go	8 cores, 16 GB RAM, 250 GB SSD	Matches Mailcow's published 16 GiB usage example and provides useful storage headroom	€32.99 excluding VAT	Best standard-plan starting point

The current KVM VPS hosting plans can be resized as requirements change. CPU and RAM can be increased or reduced, while disk space can be extended but cannot later be shrunk.

That makes a custom 8 GB configuration worth requesting for a small private installation. Until a custom price is confirmed, vm.Go is the only published ServerSpan plan that reaches a comfortable Mailcow production target without starting below the vendor's memory guidance.

Mailbox count alone does not determine storage

Mailcow's 20 GiB minimum excludes email data. It also does not represent the complete long-term storage requirement. Docker images, MariaDB, Redis, search indexes, quarantine data, logs, temporary files, updates, and backup staging consume disk alongside the users' messages.

Use this planning formula:

Required disk = 20 GiB Mailcow base + expected live mailbox use + indexes and operational data + free growth reserve.

Calculate expected live use rather than adding every mailbox quota. Ten users with 20 GB quotas do not automatically need 200 GB of live mail storage, but they can eventually reach it. Measure imported mail and define a realistic annual growth rate.

Expected live mail	Practical disk target	Suitable current plan	Reasoning
Up to 30 GB	At least 100 GB	Custom 8 GB KVM based on vm.Steady storage, or vm.Go	Leaves room for Mailcow services, indexes, logs, updates, and growth
30 to 120 GB	Approximately 250 GB	vm.Go	Fits a small business installation without beginning near full capacity
120 to 180 GB	250 GB with strict monitoring	vm.Go	Usable, but mailbox growth and backup staging must be controlled
Above 180 GB	More than 250 GB	Custom KVM storage	Provides safer growth room and reduces emergency disk expansion

The ranges above are operational planning bands, not Mailcow limits. Keep enough free space for database maintenance, image updates, temporary files, and recovery work. A mail server should not reach production disk exhaustion before anyone notices.

SMTP access changes the real monthly price

A Mailcow server needs to receive email on TCP port 25. Direct delivery to other mail servers also requires outbound SMTP access. ServerSpan blocks SMTP traffic on virtual servers by default.

The current Terms of Service allow the restriction to be lifted after successful KYC validation or under an agreement for a €20 monthly fee. A third option is to keep direct outbound SMTP blocked and configure Mailcow to send through an authenticated relayhost.

Delivery model	VPS cost	Additional known cost	Annual known infrastructure cost
vm.Go with SMTP enabled after KYC	€32.99/month	No published SMTP surcharge	€395.88 excluding VAT
vm.Go with the SMTP fee option	€32.99/month	€20/month	€635.88 excluding VAT
vm.Go with authenticated relayhost	€32.99/month	Relay-provider cost	Needs human verification
Custom 8 GB KVM	Custom VPS price	KYC, SMTP fee, or relayhost	Needs human verification

These totals exclude VAT, domain registration, remote backup storage, migration work, monitoring, and administration.

Mailcow supports sender-dependent relayhosts through its administration interface. This can separate mailbox hosting from outbound reputation management, but it introduces another service, another set of credentials, and another bill.

The broader ServerSpan analysis of self-hosted email architectures explains when direct delivery, a relayhost, or a split architecture makes operational sense.

DNS and IP reputation remain separate from server size

Buying 16 GB RAM does not make email reach the inbox. Mailcow requires correct A and MX records, and the PTR record for the server IP should match the Mailcow hostname. SPF, DKIM, and DMARC must also be configured for every sending domain.

Before migrating mailboxes, confirm that the provider can set reverse DNS for the assigned IPv4 address. Then verify the public records:

dig A mail.example.com +short
dig MX example.com +short
dig -x <server-ip> +short
dig TXT example.com +short
dig TXT dkim._domainkey.example.com +short
dig TXT _dmarc.example.com +short

The A record should return the Mailcow server IP. The MX record should point to the Mailcow hostname. Reverse DNS should return the same hostname. SPF, DKIM, and DMARC output should match the policy configured for the domain.

A DNS pass is necessary but does not prove good reputation. New-IP behaviour, complaint rates, message content, sending volume, recipient engagement, and previous blocklist history can still affect delivery. The ServerSpan guide to email reputation management on a VPS covers the work that begins after authentication records pass.

Run a preflight check before installing Mailcow

Check virtualization, memory, swap, disk, CPU, time synchronization, and port conflicts before cloning the Mailcow repository:

systemd-detect-virt
nproc
free -h
swapon --show
df -hT /
timedatectl status

sudo ss -tlpn | grep -E -w '25|80|110|143|443|465|587|993|995|4190'

systemd-detect-virt should report KVM or another supported full-virtualization platform. Do not continue on LXC or OpenVZ.

free -h should show at least the intended RAM allocation. swapon --show should confirm the planned swap space. The disk check should leave enough capacity for current mail plus growth.

The port command should produce no unexpected listeners on Mailcow's required ports. An existing Postfix, Exim, Dovecot, Apache, or Nginx service can prevent the Mailcow containers from binding correctly. Identify the service before changing anything.

After installation, inspect the stack with:

cd /opt/mailcow-dockerized

docker compose ps
docker stats --no-stream
docker system df
df -hT /var/lib/docker

All expected containers should be running without continuous restarts. Memory use should leave operational headroom. Docker storage and the underlying filesystem should remain well below exhaustion.

Backups need storage outside the Mailcow VPS

A snapshot of the same VPS is not the only backup a mail system should have. Mailcow includes a helper script for backing up mail data, encryption material, MariaDB, Redis, Rspamd, and Postfix data.

cd /opt/mailcow-dockerized

MAILCOW_BACKUP_LOCATION=/mnt/remote-mailcow-backups \
  ./helper-scripts/backup_and_restore.sh backup all --delete-days 7

The destination should be a remote or separately protected filesystem, not another directory on the same VPS disk. A successful command should create a dated Mailcow backup directory without component errors.

Backup storage is additional to the VPS prices in this article. Capacity should be based on live mail volume, retention period, backup frequency, and expected change rate. Test a restore before relying on the schedule.

Choose the plan from RAM first and storage second

Reject vm.Ready and the standard vm.Steady configuration for Mailcow because both are below the official memory minimum. Do not select an LXC plan simply because it offers 8 GB RAM at a lower price.

Request a custom 8 GB KVM VPS for a small installation with approximately 5 to 10 users and moderate mailbox use. Confirm the custom price and storage allocation before ordering.

Choose vm.Go when you want a standard published plan, expect ActiveSync devices, need ClamAV and full-text search enabled, or want 250 GB of local storage. Its current infrastructure price is €32.99 per month excluding VAT before SMTP, backup, or management costs.

Move beyond vm.Go when expected live mail approaches the usable capacity of its 250 GB disk, when concurrent connections create sustained memory pressure, or when backup and indexing jobs interfere with normal mail access.

ServerSpan's KVM VPS hosting provides the virtualization type Mailcow supports and allows later CPU, RAM, and disk expansion. Confirm SMTP access, reverse DNS, mailbox growth, and the backup destination before moving production MX records.