Depending on the subject of your communication your problem can be solved by a number of tools:
Business-object related communications
eg. code, customers, offers, tickets, blog posts
Often times there are tools focussed around the objects in question, that also have comment- or wiki-style communication and documentation systems in place.
Examples of this are:
- Repository management system that sometimes give you commenting ability down to specific lines of code
- CRMs that even let you comment on specific communication items
- for most ticket system this is an essential feature anyway
- audit/editorial systems for blogs
Ad-hoc problem related communications
eg. questions pertaining to some order that needs special handling, unclear commits, clarification of responsibility towards customer requests
These can be both formal and informal and informal parts are often handled by chat, mail, phone, yelling, etc. For communications that needs to be logged for some reason, email can work, but if you need more accountability, handling questions as tickets or in some chat-like internal communication system that is monitored and persisted is probably a good choice.
Open questions up for discussion
this can be around any topic
These questions are common and usually should be stored even beyond the time an employee or customer relationship terminates and their related accounts are closed. So requirements usually are that the data is decoupled from any accounts like email or CRM and that it can be easily accessed by new users entering the communication system.
Mostly one would use:
- wikis, because they just work
- Forum software, as permission systems on those are easier to use
- an on-premise or saas-style version of Q/A systems like this one
- lately, company-centric 'social networks' also increase in number