My app allows users to invite their friends by email asking them to join. I'm afraid that if one user invites over 200+ friends from his/her email contact list, will those emails be blocked? How do I prevent my emails from going into the spam filter?
Contact your hosting provider and ask them these questions. hosting providers will lock accounts that sends out XX amount of emails. It all depends on your host provider. Also, the spam trigger is very easy to pull and anything sent without permission from the email account holder is spam. IE can be blacklisted.
put a captcha code in to prevent bots. encrypt the html form with javascript to further prevent bots from finding your form. log ip addresses and if the user puts more than X friends don't send and put a cap in place so that IP cannot send any more mail using your form. Also append a link in the email saying something along the lines of "if you received this message as spam click here to report it"
But if I use my google smtp server, would be more safe. Does google have a limit on how many emails you can send out with their smtp server?
Yes it does, I believe its 50 per session. Using the Google SMTP is the safest bet just make sure u pause the loop or howerver ur using it every 50 emails. If you are doing it through ur host make sure u enable SPF on your domain. Another thing i would recommend is using SWiftMailer to help you out alot. It is a PHP to send mail through SMTP (you can use it to send emails through gmail or ur webhost)