Gmail – How to Send Mail to More Than 500 Contacts Without Being Marked as Spam

gmailspam-prevention

Many of my friends use Gmail. When I want to send them attractive emails, I have a group named everyone that I use it.

After that I send email to my friends, and remind them to check their mailboxes, they tell me, not delivered! But when I tell them

please check your Spam folder

They report that they've received it. Is there any way to tell Gmail to send, x mails every y minutes?