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Exchange server replacement that runs on Linux

I want to build an entirely Linux based network, forget Microsoft for good.

Can anyone suggest free software that will replace the goodies that are included with Exchange and Outlook? Ie: Mailboxes for users, calendars, email, etc. And also a mail client?


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marked as duplicate by James, Mark Henderson, Jason Berg, John Gardeniers, Zypher Sep 7 '10 at 4:45

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Free as in beer or free as in open? – Oskar Duveborn Sep 6 '10 at 19:22
You might find an "alternative", but asking for Exchanges features and scalability for free isn't a realistic scenario. Lower your expectations.. – pauska Sep 6 '10 at 19:51
I think the first thing you need to do is define exactly what it is you are trying to do. It isn't good enough to say you want an "exchange replacement" - what parts of exchange do you use? If you don't use public folders, for example, then you don't need to replace that functionality. Do you need "Exchange ActiveSync" type capabilities for mobile devices, etc? – RobM Sep 6 '10 at 22:58
@Oskar, where is do you get free beer? In Australia we are expected to pay for it. – John Gardeniers Sep 7 '10 at 3:01
@John at bars or at work generally, but I think you have to be charming too ;) Reason for the free-question is that things like Zimbra isn't gratis as far as I know. – Oskar Duveborn Sep 7 '10 at 7:33
up vote 10 down vote accepted

Take a look at Kolab, Zimbra and eGroupware, all of them attempt to replace Exchange.

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And all of them - sady - fail. Basic functionality - yes. Higher functionalty - no. Especially not when you add all the other goodies into the mix. – TomTom Sep 6 '10 at 11:37
TomTom: what goodies exactly are you after? We are using Zimbra for thousands of employees – dyasny Sep 6 '10 at 11:59
TomTom: You never know what kind of goodies people need. For basic and even for some advanced functionality all the products I mentioned can be very nice. Care to enlighten us with some of the most hottest showstopper bugs Kolab, Zimbra and eGroupware still has? – Janne Pikkarainen Sep 6 '10 at 12:02
I think TomTom is addicted to Exchange. – d-_-b Sep 6 '10 at 13:42
Went from Exchange to Zimbra and had no problems at all, users love it and its pretty easy to manage/backup/troubleshoot since it's just a lot of open source software put together with a smart glue/interface. Around 4k users. – coredump Sep 6 '10 at 18:47

Despite a nodding acquaintance with the rest of the world, MSExchange has always been modeleld on x400. There are other implementations which based around x400 out there (Lotus Notes, and until it was discontinued, Samsung Contact). However IMHO they are all a complete PITA to manage and should be avoided if at all possible.

And also a mail client?

Lets deal with that first. Presumably you mean a client which will provide the users the functionality they have in Outlook. Well, Outlook is probably a sensible starting point. Although Microsoft tend to hide this information away, it will happily talk SMTP, POP, IMAP, LDAP and iCAL.

Indeed it probably makes a lot of sense to plan an LDAP system (or extending your current provision) to provide address book functionality. If you don't already have a suitable LDAP server, have a look at GOSA. Note that if you have multiple sites, then you should really really have LDAP based mail routing set up.

Of course, using open standards for server protocols mean that you can choose from lots and lots of user agents - e.g. you could easily add web based clients for mail and calendar, e.g. squirrelmail, Mozilla calendar (but there are many, many more).

Serverside you need to have a Mail Transport Agent - several years ago I did some research on this and found that Sendmail and Postifx were significantly more effective at sending email compared with Qmail, Exim and others (MS Exchange was bottom of the reliability list). Although Novell's groupwise proved just as reliable.

I'd recommend using an IMAP server in preference to a POP server. There's lots of good ones out tere scalable up to massive levels. The UoW one usually comes bundled in distributions but you probably need something a bit more sophisticated if you have more than 200 or so users - dovecot or courier maybe.

There was an open-source project attempting to reimplement mapi as a standard API but AFAIK its not been very active lately.

In addition to the products mentioned by others, you might want to have a look at sogo

Your not going to get all the answers here - you're still going to have to do some research and probably try integrating different products - but the maintenance effort will be massively reduced. There's some links below to get you started. - iCAL stuff - LDAP stuff

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However if you go this way Outlook doesn't implement shared calendars in the way that Exchange does. This may be a dealbreaker. – pjc50 Sep 6 '10 at 13:06
@pjc50: yes - and there's lots of other differences between the behaviours of the different implementations of products even when delivering a very well defined requirement (e.g. consider the situation with browsers). But without doing several weeks of analysis I can't tell which of those are relevant. – symcbean Sep 6 '10 at 13:35

The IMHO best alternative hasn't been mentioned in this thread yet. See below. :-)

I want to build an entirely Linux based network, forget M$ for good.

Is that a rational decision serving your company's best interests? I'll leave that question to you, but having a negative emotional reaction towards Microsoft isn't a good reason to disregard their products.

Can anyone suggest free software that will replace the goodies that are included with Exchange and Outlook? Ie: Mailboxes for users, calendars, email, etc. And also a mail client?

There is no 100% replacement, but Google Apps comes closest, and has most momentum of the Exchange competitors.

  • It is Linux based, in the sense that Google runs on Linux, and it is very easy to get started with.
  • It has good support for open standards, f.x. IMAP over SSL for the Thunderbird & Outlook email clients.
  • Google Apps has excellent device support (iPhone, Android phones, etc) as well. And of course
  • It is a fully managed solution, with built-in spam filtering, antivirus, backups etc, leaving less work for the customer IT staff.
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+1 for SOGO. Active development, lot of features, good community.

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I didn't see it mentioned so I thought I'd add PostPath. I haven't personally used them but I've heard they offer easy integration with existing Microsoft environments. Something like that might make transitioning a bit easier.


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i suggest Open eXchange :

There's a Community edition and a commercial edition.

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Let's face it, you wont get the full Exchange feature set for free, but for a much better price. Especially the fat client will be a real problem if you want to have all the functions an Outlook / Exchange combination will offer you.

I had some good experience with Zarafa in the past and even Scalix did the job in small environments (a different story with medium and large installations...).

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