How users can unsubscribe form getting e-mail messages form the board?

Kirill, Moscow

By unchecking email subscription option.

Where is it? I can't find

if you're registered user and you recieve email notifications from the topic you've chosen. In this topic under the post form you have a checkbox which manages subscription.

If you are admin and you don't want receive notification about every post users make to your forum change $emailadmin=1; to $emailadmin=0;
in your setup_options.php
Anyway RTFM.

Sergei
btw
My provider does not support email. So I turned email notifications in setup_options.php off.
When a new user registers, then the following is displayed:
Warning: mail() has been disabled for security reasons in /.../.../.../ bb_functions.php on line 1508
Is this right ?

yepp your provider has disabled mail function. if you don't want any errors to appear write this line:
error_reporting(0);
in index.php for example.
Or ask your provider to enable mail function for you

Thanks!

Kirill: when registered user subscribes to the topic, he can see "Unsubscribe" link instead of checkbox.