What corporate messenger would you recommend?

Question

Computer networks

Recommend a corporate messenger (more than 100 people). Basic conditions/wishes:
1) support for desctop version of windows
2) support for android
3) Synchronization of history on all devices
4) History is stored on the server indefinitely (ideally - on ours)
5) support for group chats (in general, the main wish is group chats. Create groups of contacts Access to past group chats at any time and without problems It is possible that there was a group chat tree
6) I would like a corporate version in which each person is provided with an internal contact, after possible leaving access to the account and the entire history of correspondence remains behind the company.
7) File sharing
8) Quoting ability
The main criterion is the focus on group chats (maximum convenience and comfort) Thank you!

Answer 1

I do not want to seem "original", but Skype is suitable for almost all points.

Answer 2

Why Skype is not suitable:
1) In group chats, there is no way to merge 2 previously created chats with the transfer of correspondence to both parties before merging.
2) In Skype, at times, very bad synchronization (a message came to the PC at 2 o'clock, on the phone at 3, on the tablet at 4)
3) I would like to be able to save each group conversation separately. Those. not 1 group and all discussions in it together, but creating topics, discussion, later easy access to it, resuming work, providing access to other employees (who did not participate in the correspondence)
4) On the phone - lg g2 when a message arrives on Skype - I only see it when I open skype, it doesn't hang in the background.
5) Possibility in the existing group to select several subgroups for some messages
6) no integration of other IMs
7) Ability to integrate IM into GTD
Main focus on corporate work through a large number of group conversations. Thank you!

Answer 3

XMPP server, such as OpenFire
on client sites any clients - to the taste and color of the user (QIP, Pidgin, etc.)

Answer 4

Microsoft Lync

Answer 5

VIPole - encrypts on the computer, has a passphrase, secure communication channel, cross-platform. There is a free version + if you need a corporate server, then they will install it on the company's servers.