For a while now you could have noticed issues with the e-mail system, which was often times down. Also, whenever an email from this website was sent, it would be tagged as “This message may not have been sent by”. As of today, the issues should be fixed permanently.</p>
The reason why the messages were tagged is that when sending mail through a PHP form, you can select to send from any address, real or not. Since GMail keeps track of authentication details, which are not present when the message is not sent through Google services, it notifies everyone who receives the email that it might not have come from the right source.
The solution to this is to actually send the mail through GMail servers, which append the needed authentication information. In addition, it frees the internal website mail server from having to do that much work, making use of Google services instead. So from now on there should be no more e-mail related issues (unless, of course, GMail itself goes down).
That said, lately the email server on the hosting server has been active, so I could get notifications about every new comment and receive inquiries from the contact form. This update should just solidify the service, and get rid of the scary notification in all received emails.
If you have registered on the website, but haven't received a confirmation email, please ask me in the comments of this post and I will activate the account for you. For new registrations such measures should no longer be necessary.