Hi,
I remark that when a user register it takes more than 30minutes to mail (activation mail) arrives to him! I have forums and the mail arrives immediately to users! Why?
(sorry for my bad englisth)
the email is sent out immediately from the script. What happens then can't be said. This is a matter of server setup and the way email is being delivered over the internet. Depending on the configuration of all mail servers in the chain and the clien't config, it can take some time untill the email arives at the client. Email is not a "live" medium (a standard fax machine without storing and delayed sending features for example is "live"), it can take some time untill the email is being delivered, it just seems to be "live" for some emails.
Your question is not related to coppermine at all, you might want to find out how email works in general. A good place to start is http://en.wikipedia.org/wiki/Email#How_e-mail_works
Joachim