Cannot send email user name or password is incorrect
I have an iPhone 3Gs with 6.1.6 iOS software and gmail. Until last week I could receive and send emails on my phone. Last week I tried to email a photo from my iPhone and received the following message "Cannot send email the user name or password is incorrect". About 30 minutes later I received an email message from google accounts with a sign-in attempt blocked message. Since then I have not been able to send an email from my phone. Every time I try to send an email I get the "User name or Password for Gmail is incorrect" - message. I changed passwords but that didn't help. I can receive emails on my phone but I can't send them. The only way I can send email is by clicking on the less secure apps button on the google accounts settings page.. Why do I get this message now and how can I get gmail working on my phone like it used to? If I delete my gmail account does it just remove it from the phone where the same account can be reinstalled or is it completely gone for good?
iPhone 3GS, iOS 6.1.6