Allow users to send files

I have configured an Asterisk server and its working perfectly, now I want my users to send files to each other, in case if the recipient is offline, server should save the file and forwards it to recipient once they are online.
Can anybody suggest me which external service i can use for this purpose… Thanks in Advance.

Email server?

I donot want them to email, rather they can transfer file directly between each other.

You will need to do that outside of the telephone system.

Can you suggest any other server that can allow me to achieve this functionality…

Some IM servers support it. I’d look into an XMPP server.