Mail Stack Options and Features

E-mail is an undisputed essential service of the Internet. If you or the organization you're working for is deploying ClearOS with the intention of providing e-mail services, this document is for you.

ClearOS is all about choice - choice around where you deploy services (in the cloud, private cloud or on-premise), and choice in terms of what tools you use to achieve a desired objective. No where is that choice more pervasive than in selecting mail services under ClearOS. The goal of this document is to:

  • list options available for running SMTP under ClearOS
  • what apps are free and what are paid apps that are optional
  • what are best practices for implementing each solution

On-Premise/Private Cloud vs. Cloud

At the highest elevation of decision making, deciding where to run your mail services trumps all. While there are practically an unlimited number of vendors offering hosted mail solutions based on dozen's of platforms, if you're reading this document, we're assuming you're interested in taking advantage of apps and services available via the ClearOS Marketplace that can help you achieve your goals.

For purposes of clarity, an on-premise or private-cloud implementation of a mail stack is classified as apps and services running directly on ClearOS. Linux, known for its security and stability, powers much of the Internet's back-end infrastructure, including mail services. As such, ClearOS is an inherently 'good choice' as a platform for hosting your mail server and accounts.

Where you choose to physically deploy ClearOS is the origin for the differentiation “on-premise” or “private cloud”.

On-premise represents those installations that are physically located within a company's point of presence - a store, office, school etc. Many small businesses choose to run the mail stack on-premise, taking advantage of cost savings and accepting or mitigating services like redundent Internet connection, physical security measures, power backup etc. that a hosted solution provides.

Private cloud refers to ClearOS implementations that are physically located in the cloud - typically cloud-services such as Amazon's EC2 or Google's Cloud Compute or a datacenter dedicated to providing Internet connectivity and space (either virtual or physical) for running a server. Larger companies may have co-located within at a datacenter. Smaller companies can lease space or virtualized servers for running dedicated mail stack based on ClearOS in the cloud. The term private-cloud is typically used in this case since ownership of the infrastructure is completely private - no advertising 'bots' or rogue employees have access to your mail.

On-Premise/Private Cloud

At the current time, there are four integrated options available for an on-premise or private cloud deployment of mail services: * OpenSource Mail Stack * Zarafa Community Edition for ClearOS * Zarafa Small Business Edition for ClearOS

OpenSource Mail Stack

For over 10 years, ClearOS has provided tremendous value by integrating the best-of-class software for providing a mail stack that is stable, secure and simple to configure. This history lays the foundation for the open-source mail stack. As its name implies, the solution is comprised of various software written by a diverse group of individuals and organizations under similar OSS licenses.

For those interested, the following table provides details on the software/project that provides each service or feature in the OpenSource mail stack.

< 100% 20% 30% 50% >
Feature/Service Company/Project Home Page
SMTP Postfix
IMAP(S) Cyrus
POP3(S) Cyrus
Antimalware/Antivirus ClamAV
Antispam SpamAssassin
Message Handler Amavis-New
Greylisting Postgrey
Mailbox Backup ClearCenter
Mail Archive ClearCenter Available
Webmail Roundcube Available
Mobile Sync N/A N/A
MX Backup ClearCenter DNS
Just because a feature is listed as Not Applicable in the table above does not mean it cannot be done. It simply means it has not been integrated into the ClearOS framework and Marketplace so it cannot be installed with a few clicks of a mouse. However, if you have the knowledge, there is no shortage of software (both open-source and proprietary) that is compatible with ClearOS and can be installed manually.

Zarafa Community and Small Business

In early 2012, ClearCenter partnered with Zarafa (, the leading open-source Exchange server drop-in replacement. Zarafa's ZCP (Zarafa Collaboration Platform) brings many great features to the mail stack, including a stellar webmail UI experience, calendaring, notes, groupware services (shared folders, calendars, notes etc.) and archiving.

Zarafa actually uses many of the same open-source components that drives the Open-Source mail stack described in the previous section. In fact, the only change is the Cyrus IMAP/POP3 service being removed for Zarafa which provides its own implementation of these protocols.

The table below provides a brief summary of the differences in Zarafa versions licensed under the ClearCenter/Zarafa partner agreement.

< 100% 40% 20% 20% 20% >
Feature/Service Community Edition Small Business
Intended Use Private Use/Home Business/EDU/GOV
ClearCenter Supported No Yes
Zarafa Supported No Yes
Outlook/Exchange Support 3 Users Yes
Advanced multi-user calendar No Yes
Pricing Free $14/user/yr
Mail Archive No $95/yr
For a complete description and feature matrix breakdown, please visit the Zarafa product pages here.


While options such as Office 365, hosted MS Exchange or IBM's SmartCloud are all valid options, for the purposes of this document, we focus only on GoogleApps. ClearOS has a Google Apps syncronization app that makes an on-premise implementation of ClearOS (for non-email services like file sharing, user directory etc.) that allows an administrator to provision GoogleApps accounts to users when adding/modifying users on the local ClearOS installation.

Pricing, Setup & Configuration


If you're using ClearOS Community or Professional Edition, we've made it easy to quickly select apps from the Marketplace that are required for each of the mail stack options discussed in the sections above. Each option has been 'tagged' with a unique marker, as listed in the table below. These same tags have been applied to each Marketplace app that, when combined, provide the mail stack as described.

To lookup an option in the ClearOS Marketplace, type in the tag in the search field. Ensure no other filters are set. Select all recommended apps and click on the “Install/Upgrade” button to proceed to the Marketplace confirmation.

< 100% 40% 10% 20% 20% >
Mail Stack Description Tag ClearOS Community ClearOS Professional[1]
Open-Source, Free Solution 01_SMTP Free Free
Open-Source, with additional AV/AS Updates 02_SMTP $120/yr $0 (Included)
Zarafa Community Edition 01_ZARAFA $10 $10 [2]
Zarafa Community, with additional AV/AS Updates 02_ZARAFA $10 + $120/yr $10
Zarafa Small Business, with additional AV/AS Updates 03_ZARAFA Not available $14/user/year
Google Apps 01_GOOGLE Not available $100/yr [3]

[1] Pricing based on having a ClearOS Professional Basic or above subscription (not valid for ClearOS Professional LITE).

[2] Zarafa Community Edition is not a supported app under the terms and conditions of the ClearOS Professional Edition. If you are interested in a ClearCenter-supported mail collaboration suite, select Zarafa Small Business.


content/en_us/kb_o_mail_stack_options_and_features.txt · Last modified: 2015/10/06 18:22 by dloper