If people register to my website, confirmation email always go into their antispam folder (lost about 70% of users).
If i send mail to my users, their email always go into the antispam folder (lost about 60% of messages).
why ? :(
thanks for helping :)

check what are you sending to your members, maybe that's the answer.

I don't have a specific answer for you but it is worth noting that as a general email user I have learned to check my 'spam' folder regularly in the workplace because the workplace server has it's own spam filter and sometimes sends things I want into the spam folder.

By checking what is in a spam folder a user can correct an incoming mail detected as spam by clicking adding the address as a 'safe' one...so perhaps you could add a block to your site suggesting that if the confirmation email does not arrive users should check thier antispam folder and make the necessary correction.

This is just one of those things we have to learn to do as a result of the way spam filters work - they are not infallible so we need to teach them some things.

HTH

Whatever the case, XOOPS is not the culprit... There are may reasons this could be happening depending on what type of spam protection your users have.

There is a chance that your e-mail server is acting as an open relay... if this is the case (not using some type of Auth, &/or no SPF (sender policy framework) ) your server can be listed in one of the many 'blacklists' that commercial entities use to control spam. You can start by checking to see if your server is listed in orbs by following the link below...

Check your server at ORBS

read up on ORBS at the link above, & look at your email server settings.

Another place to look is the top center form at DNSstuff.com titled "Spam database lookup" it will search your domain or IP in all the spam databases.

HTH.