I am working with email function and found that the mail which i am trying to send are collected as a spam mail my gmail , i try to change th return_path to my email id, alos try to set it as true
Most obvious reasons for Google marking something as spam is: - no reverse lookup for the sending email server - no or an invalid reverse lookup for the MX domain (and no SPF records present)
and not with the contains of the mail (for as far as Fuel is concerned, I can't speak about the email body).
There is no link between this issue and FuelPHP framework. This is due to the IP address and/or domain you are using to send mail.
On thing that could be a cool feature to be added to the email package of fuelphp (and that can help preventing your emails being sent to Google spam folder) : DKIM support.
This is usually done at SMTP server level, but for those who do not have the skill nor access to server config adding it to the framework can be really helpful.