As it is not very obvious to Registered Members of the forum that each user has their own little section where various options can be changed, here are a few details that may assist you.

I would suggest that Registered Members go to their user data section on the Message Board and make sure the options which are available are set as you would like them.

How to change your options
In order to change your options, you first of all must be logged in, then you will notice your user name appears near the top of the page, this is a link to your user data area where you can change your options. When in this area you will see another link titled "Edit user data".

Private Messages
By default when a new member registers the setting is NOT to "Show e-mail link".
If you can not find an email link (envelope icon) next to a message posted by a registered member, it means that the member in question has either decided not to "Show e-mail link", or has not changed this option in their user data section.

Your email address is not shown
In order to protect you from spammers and email harvesters your email link does not show or link to your actual email address. A contact form is used and at no time is your email address available to the sender.

Even if a registered member has not made his email link available, another registered member can send a Private Message to this person by clicking on the members username next to his message, then you will see another link "Personal message to (username)". This is providing the member has "Accept personal messages" set to yes.