2019 - I hardly see any use anymore. Other manufacturers either had a client, which is not being maintained anymore (Zimbra - still no new client, despite announcements - old client getting worse and worse), Icewarp - for Windows it's a clone of EMClient. Kopano does offer a "client", which is just a local rendition of the webclient, w/o any offline support.

Thunderbird has plugins for Calendars and Contacts via ActiveSync and would work on any client.

Stick to the core: Secure mail server, decent / top notch web client.

Now you see all the sides... I agree with Jack on his last comment. :) "A light client that works on all platform is high recommended!" November 21, 2015.

Many people loves Outlook and in general client sw installed by default on their computer/mac. You should also integrate Axigen with Outlook and Mail for MAC world. Customers cannot choose Axigen for this limitation. Webmail is great, but managing multiple users from the same windows is not possibile at the moment.

I'm using Axigen for a years and have to say that WebMail is much better then any other mail client. I tried Evolution, Thunderbird, MS Outlook and now using Mac OS Mail. It is all great clients but it is difficult sometime to get all Axigen features to client. I can not get address book or notes without additional configration of Cal/CardDAV.
So, I think it could be a goos idea to "spin-off" WebMail to standalone mail client with local storage and connection configuration. I suppose that WEbMail Proxy service works similar to demanded application behavior (it's true that local client is a proxy indeed), you just need to cut-off all non-proxy features and build a new binary. Access to the client could be via browser for a first time, but next you can integrate it with Chrome engine or something else.
It will be the best alternative to MS Outlook!
What do you think?

I personally see no benefits. I think that Web Client is best, it's also easier to develop for and uses less resources on the clients computer.

Stick with Web Client development.

Key limitations with the current offerings:

i) Thunderbird and related clients - works well for e-mail but no support for accessing\synchronising contacts, calendar or notes. Whilst there are some third-party plugins which partial address this, they take time to configure, not officially support axigen and as a result tend to be flakey. Some webmail features not available (e.g. temporary mail aliases)

ii) Axigen web mail - works well for a single account whilst online. Offers full axigen feature set (e.g. temporary mail aliases). Not possible to open multiple accounts simultaneously (without using multiple browsers). No offlline mode possible.

iii) ActiveSync clients - whilst ActiveSync clients work well on mobile devices (android\iOS), the desktop equivalents don't work well: Outlook activesync does not work with Axigen (gives connect error); emClient displays some oddities (e.g. all e-mails appear flagged); Windows 10 mail client works with occasional random temporary errors but the mail client does not always render html mail correctly. Some webmail features not available (e.g. temporary mail aliases)

iv) Outlook plugin - generally works well but Outlook can be unresponsive whilst background syncing a lot of e-mails. Works in offline mode well (providing you remember to change the default settings from download headers only). Includes calendar, note and contact support. Not possible however to open multiple accounts simultaneously. Some webmail features not available (e.g. temporary mail aliases)

Introducing a Axigen standalone mail client would side-track resources from the mail server as main priority. I do not recommend looking into an email client. There are a number of free Thunderbird alternatives out there and even MS Outlook is cheap today. By the way, you can open winmail.dat attachments in Thunderbird, there is a free plugin for it. Just Google for it.
So, please do not waste time on this.

Thanks

also some attachments created/sent with MSOutlook is not readable by webmail and thunderbird. e.g. winmail.dat, our clients are forwarding this file to us and open it with MSO and send back to them in plain format. If Axigen can make this feature available with Axigen Mail Client, then you rock the world. :)

sometime other third party mail client are annoying and hangs up.

Nice idea. Many MAC are spread around and at the moment Axigen does not support native integration with other email client. A light client that works on all platform is high recommended!