Ok.
1. I deleted mail.mydomain.com from CNAME records -I have to add that i saw a new one with "www.mail.mydomain.com" Type "A" record. I think it's related with subdomain.
2. Anyway, now there are only three records: site.mydomain.com, belge.mydomain.com, and takvim.mydomain.com as CNAME type records.
3. I could not delete any subdomain since there it says: No Subdomains are configured, in Subdomains section. There seems to be no subdomains, i think.
BUT!
I see two domain names in Create a Subdomain section! One is mydomain.com other is mail.mydomain.com! How did it happen?
Also It's the same in MX Entry Maintenance section!
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I can send and get emails with aspmx.l.google.com MX Entry for mydomain.com right now.
Problem is that I don't want to see this mail.mydomain.com domain in those sections. I just want when I enter the url, mail.mydomain.com, it should redirect me to google apps' gmail. That's all.
What should I do now?