I have just found a free phpbb forum script and uploaded it to hosting. Afterwards, I have found email sending bug! When users register at website the registration is performed properly itself, but welcome email is not sent! Also, all registered users need to login twice before to open a topic! Could you please advise on how these issues can be solved?

1. Are you using the latest phpbb version? If not get the latest from phpbb.com
2. Check your cookie settings for login problems, from phpbb's admin area. Cookie domain should be "yourdomain.com" and Cookie Path should be the directory phpbb is installed in, such as "/forum/".
3. Check if your host supports the php mail() function. Many free webhosts do not support it.

I hope this helps

you may want to check out phpbb forum and do a search:
http://www.phpbb.com/search/?q=confirmation+email