For Outlook lovers sogo and webtop provide EAS:
http://docs.nethserver.org/en/v7/sogo.html
http://docs.nethserver.org/en/v7/webtop5.html#device-synchronization-with-activesync-eas
You are right about the weak IMAP implementation in Outlook but for just mails it should be enough.
Another option is caldav synchronizer.
Hence why a drop-in Exchange replacement is valuable–the client software is already written.
Regarding Exchange alternative: Exchange is more than “just Mail”. It can also do the following things (and of cause much more):
Outlook is the favorite client for this, because it is able to handle all this stuff. Especially Mail, Calendar and Contacts is a combination where I don’t know another good software. I also have no problems with IMAP and Outlook.
Regarding replacement of a SBS:
If you build a complete new infrastructure on a green field and you are planning to use what Nethserver can do, I think it can be a good alternative - but not a replacement!
When you just have some Windows PCs without any Windows Servers, you can use it. If you have some Windows Servers and in general about all of your environment is based on Windows, you should use Windows at least for Useradministration (Active Directory), DNS and maybe also DHCP. You can still use Nethserver for Mail-, Firewall- and Webservices. That is how I am using Nethserver and it is running very well like this.
For a small company like mine, NS is a good alternative to MS SBS. It does all we need. We use eM-Client as Outlook-alternative in combination with SOGo (IMAP, CalDAv, CardDav). Our needs are covered. Also with Thunderbird (mail, calendar) it works good for us.
Not every enviroment has some hundret clients, multiple subnets and needs all the stuff MS-Servers offer. I prefer a simple system I can handle myself. Maybe it’s not perfect, but I have my costs under control.
And last but not least, I became a linux lover first with SME and than with NS! 
Fully agree.
I’m using nethserver on one of my projects, they are 250 people and it works superb.
I agree that there’s still work to be done, but paid support is good and the system is stable.
I was thinking while reading this thread and I can see that a number of managers and CxO level execs would like to see this sort of tick box comparison list as it would supposedly make it an easy decision for them if they see enough correlation between the two.
If I may throw the cat among the pigeons and say that that may not be the best way to look at it.
A better way would be to have a look at your business requirements and business needs; list them out into clear, logical and defined points and do a tick box exercise there to see if Nethserver will meet the requirements.
That way, you will have a clear idea and understanding if Nethserver will be able to match your business requirements and meet your business needs.
If you do a tick box exercise of Nethserver against Microsoft Small Business Server, all you get is a comparison of some sorts between the two without necessarily a clear indication of whether it will meet expectations or your business requirements.
Its a bit of a different way of thinking for the techies but most managers and CxO level execs should (in theory) understand that concept of checking the alignment of a product to their business requirements/needs.
For most small businesses, their users are Microsoft trained. They need outlook, they need roaming profiles, they need acl’s like they know them and they need Microsoft trained engineers to manage it, as they are cheaper then Linux guru’s.
If you can replace the small business server with Nethserver and have them not notice, you have an instant win on the licensing costs for that domain. If you can’t, you have a whole lot of convincing and training to do 
Hi Rob,
I know my answer comes late, but in my opinion IMAP integration at Outlook is not very good.
For example the sent mails often are only local at Outlook 2013 and 2016 (if you configure the account it searches for the directories at the server, frequently it didn’t get them and you get a folder “Sent (only this computer)”. If so, you have create a filter to move them to the right directory.
For drafts you don’t have a chance with a filter, you have to move them manually.
I think things like autoresponder you can’t create at Outlook with IMAP (If this is not the case, please say me how, I miss that for my customers).
OK… I fixed it:
Outlook and IMAP can work like a charm, but caldav will not work. You can only add an ics based calendar, which means it is read only to you. This is usually unacceptable.
I have found that using activesync for mobile devices works like a charm, except some mail clients can not properly handle shared calendars.
Using outlook 2013 or 2016 with ActiveSync works, but loads of special effects are had at the moment.
Using outlook 2013 or 2016 with IMAP works like a charm, but calendar is limited.
Using Thunderbird with IMAP and caldav, works like a charm.
I have a customer that wants to use Outlook with Webtop via IMAP. it’s a PITA…
For synchronizing Outlook with CalDAV and CardDAV servers there’s this plugin:
Hi alefattorini,
I think that With NethServer v7 together with Webtop can be a very good alternative for SBS as soon as there is a solid integration with MS Outlook so that all functionalities of Outlook can be used. I have users who only wants to work with MS Outlook because they are used to it and benefits it offers as soon as they are offline.
IMO the only reason to use Outlook is the integration with Exchange and the MAPI protocol. Since NethServer nor webtop support the MAPI protocol, there is little reason to use Outlook. If you were to use a mail client, I would look elsewhere.
However, I know people are not easily made to change. So use Outlook with IMAP and it should work.
As @planet_jeroen already mentioned, try to get your users to use TBird/Lightning. It works like a charm.
I don’t agree.
I am a long time Thunderbird user, and i love it, but in several things Outlook is far more powerful, starting from the storage capabilities (with current PST format you can easily scale to tenths of gb, using maildir format the limit is still at 4gb), contacts management, programmability (rules, which are pretty powerful compared to Thunderbird, and easier to create for |users), personalization, form creating.
It has also some limits (IMAP management, IMAP folders just like MacOSX Mail or iPhone), you have to buy windows and outlook for use it. But it has more than one points more than thunderbird.
Hi Rob,
Thanks for the information about Thunderbird / Lightning. I’m going to try it out and discover what the differences are in relation to Outlook. Outlook with IMAP is not a pleasant combination for someone who is used to Outlook and MS Exchange, so I hope thunderbird / lighting will be a good replacement for Outlook.
Hi Pike,
I think you have good arguments there. Fortunately, not every user needs all the Outlook functionalities, so I think there are plenty of opportunities to introduce NethServer where MS Outlook is not needed, especially if you will use Webtop in a web browser. And in addition, you also have the Webtop integration with Netxcloud, which is an excellent function. However, I believe that if Outlook were fully supported by NethServer, NethServer would be the absolute alternative to MS Windows and MS Exchange for Small Business and not to forget Office365.
I think that current workgroup policy for Nethesis and this project is “clientless groupware”.
Therefore, Outlook will be considered only as imap client, nothing more.
really? strange enough, I’m currently using a 20 GB account on TB with no issues at all… can you give more details on this limitation?
interesting, I feel exactly the contrary… where I work I’m forced to use outlook and it’s like an elephant inside a crystal’s shop.
TB has thousands of plugins, you can use it for almost everything… and it’s native search feature is far better than the outlook’s one (which uses windows indexer service… which can create on a heavily used server, a 600 GB .edb file…)
TB can run on every O.S., so you can move from windows to linux and vice versa without issues (as I usually do with my home pcs)
this morning, back in the office, I had no access to outlook 'cause its local profile was corrupted (doh!)… never had such a problem with TB in dozens of installs and in 10 years…
I have customers using (8 users at the same time) shared imap accounts with more than 30 Gb of mail… no issues, never.
and I can use almost any release of TB to access my linux servers, I’m not forced to buy another newest release when I upgrade my server or my pc.
the real PITA is that TB is not intended to be mass deployed in a enterprise environment, 'cause it lacks some features (on admin side, I mean)…
Ah, I forgot… TB has also some logs… I know that from a simple user’s POV it doesn’t mean anything, but when I’m asked to understand what’s going wrong, I prefer to read some logs instead of search for strange and useless error codes out there.
last release of Outlook can connect to SOGo’s activesync
and with some free plugins (ops, addons) you can force outlook to use caldav/cardav
there is no exchange replacement out there for free… and outlook, without an exchange server, is just an useless email client…