How to fix **Swift_TransportException** in Laravel 5.6

I am going to send contact form details via the gmail. My .env file is look like this,

MAIL_DRIVER=smtp
MAIL_HOST=smtp.gmail.com
MAIL_PORT=587
MAIL_USERNAME=myname@gmail.com
MAIL_PASSWORD=password
MAIL_ENCRYPTION=null

but when I send submit buttons following error is coming,

 (1/1) Swift_TransportException

Expected response code 250 but got code "530", with message "530 5.7.0 Must issue a STARTTLS command first. u5-v6sm3569015pgk.46 - gsmtp
"

then How Can I fix this problem?

via Chebli Mohamed