I think the Tiki Webmail manage (existing) mailboxes but it does not create email address (unless you use in an innovative way the groupmail feature that can be attached to it ). It is working fine and can be one part of your "offer" to your user but still, to create real email address and manage them you will need to dig on the mail server setting side (or subscribe to a mail services provider like Zoho Mail - not related to them).
Can Tiki allow members to send and receive emails from within Tiki?
There is in Tiki a Message feature that give users (groups) a full send/receive messages system without the need of a different or new email address (notification of a new message can be sent on the user existing email):
Hope this helps!