Gmail Marks Emails As Spam

Hi.
Gmail sends emails sent from the server to spam, although all the checks passed successfully in the email properties.

On other mail services such as Yandex and Mail.ru this does not happen.
Adding a domain to postmaster.google.com did not solve the problem.
Is there any way to solve this problem?

Please check that you have a ptr record from the ip to domain name the server is sending mail out from

From google themselves:  https://support.google.com/mail/answer/1366858?hl=en

You need to know why they are marked as spam to clear them up.  You may need to contact google to get your IP out of the gray list.

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Why emails have spam warning labels
Gmail automatically identifies suspicious emails and marks them as spam. When you open your Spam label, you'll see emails that were marked as spam by you or Gmail. Each email will include a label at the top that explains why Gmail sent it to Spam.

Spoofed email addresses
Phishing scams
Messages from an unconfirmed sender
Administrator-set policies
You tried to unsubscribe from this sender
Messages content is empty
Messages you sent to Spam

Graylisting shouldnt cause this though  it would really only force the sending server to retry before delivery is accepted at a protocol level (it will cause the message to be temporarily "rejected" until the sending server tries again after a determined time frame)

Google maintains an internal "Gray List" of hosts that it has not blocked, but monitors for spam.  If your server is on that list, they pretty much mark everything you send as spam.  That's what I was getting to. 

Google wouldn't know a true graylist if it hit them square in the face.  They do what they want, even if it goes against RFC.

Hahahahahah yes iv noticed they think they're the only mail providers allowed to send mail (-;

Please check that you have a ptr record from the ip to domain name the server is sending mail out from

PTR record is and it is correct. When installing the server, we asked the provider to make this entry for us.
Checked our IP for being in blacklists, but everything is clean there.
I already wanted to contact Gmail, but I just won’t find an address to write them a letter.

Seeing as your not blacklisted, your best option would be to have people mark your email as "Not Spam", and hope you get some reputation with the almight GMasters.

Hi.
Gmail sends emails sent from the server to spam, although all the checks passed successfully in the email properties.

On other mail services such as Yandex and Mail.ru this does not happen.
Adding a domain to postmaster.google.com did not solve the problem.
Is there any way to solve this problem?

Did you manage to solve this? I have the same problem. I think it is a problem with key length DKIM 1024 and gmail accepts better 2048, I did a comparison of cwp7 and cpanel and the only difference was the DKIM, and in cpanel there was no spam problem