dns manager settings

It could be DNS, but given that Gmail is actually accepting the mail I would look elsewhere. The content of your messages may look suspicious, in which case you can modify what they say. Recipients on Gmail may be flagging your messages as spam, in which case you should not send mail to those users and should ask your other users on Gmail to mark your messages as "not spam" to improve your reputation.

For my own domain I only send few messages to few people, and asked them to mark my messages as "not spam", wich … didn't help.

Why should my content look suspicious ? I only write normal letters. I can't tell all people on different domains on my server to rephrase their content to pass gmails filters :D

I found out a PTR record was missing, so I already added that. But that doesn't solve the 3 DNS issues of my server.

Getting mail reliably delivered from your own server is a tricky task and to save the bother I would recommend using a third-party service such as Mandrill. It can be configured at server or application level.

Mails are not even sent by my server (it's the local internet provider that takes care of smtp). But it seems a PTR record is needed for reliable mail delivery to check the domainname, so that solved the reverse DNS lookup already.

Now it's just the intodns.com problems that need to be solved.

Can someone help me out with this ?

According to your registrar, your nameservers are ns1.linode.com through ns4.linode.com.

Domain: webfoundry-hosting.be
Status: NOT AVAILABLE
Registered:     Wed Feb 26 2014

Registrant:
        Not shown, please visit www.dnsbelgium.be for webbased whois.

Registrar Technical Contacts:
        Name:   Hostmaster
        Organisation:   Nucleus BVBA
        Language:       nl
        Phone:  +32.32750160
        Fax:    +32.32750169
        Email:  support@nucleus.be

Registrar:
        Name:    Nucleus
        Website: http://www.nucleus.be

Nameservers:
        ns3.linode.com
        ns2.linode.com
        ns1.linode.com
        ns4.linode.com

Keys:

Flags:

Please visit www.dnsbelgium.be for more info.

You should add ns5.linode.com on your registrar's list of nameservers if possible. If it is not possible, don't worry about it.

You should remove ns1 and ns2.webfoundry-hosting.be from DNS and deactivate the nameserver on your Linode; there is no reason for you to run your own.

You should remove the MX record pointing to server.webfoundry-hosting.be; it is a worthless duplicate.

Your SPF record currently only designates your Linode as a permitted sender for @webfoundry-hosting.be mail. Mail from all other hosts is considered a softfail. Update your SPF record if other hosts legitimately send @webfoundry-hosting.be mail.

It seems unlikely that any of these changes will actually help, but they answer your question.

Thanks Vance for all your time and effort !

Indeed it will be unlikely that these changes will solve any mail-issues, but at least the settings will be "as they should be" and get rid of those pesky red issues on intodns.com wich troubled me.

Just one last small question … if I remove ns1 and ns2.webfoundry-hosting.be from DNS and deactivate the nameserver on my Linode … will my users still be able to register their domains using these nameservers? (they are still defined in DirectAdmin and my server).