when some one register in my site ît send comfirmation email. But the email is going on spam folder why gmail detect it as spam? is there any solution it never go in spam folder it should always go in inbox
Check if your IP is blacklisted in any of the blacklists (RBL & DNSBL), Also verify that you have PTR (Reverse) Records set for your IP.
in addition to checking if your IP is blacklisted and setting up a valid PTR record for your IP, you may also want to set-up opendkim and I'm sure the emails will not end-up in the spam folder.
Make sure you have SPF records enabled as well as DKIM. Is the IP you're sending from on any blacklists? What type of content is inside the emails?