SMTP From address may not be blank: nil rails action mailer

This error because of the default hash in action mailer. Default hash is from address to mailers.

for below mailer it don't have any default mail address. But my case, i created a application mailer is inheriting from ActionMailer::Base.

class ApplicationMailer < ActionMailer::Base
  default from: "xxxxxxxxx@gmail.com"
  layout 'mailer'
end


class PostCreate < ActionMailer::Base
   
    def user_post(user)
        @user = user
        @post = @user.posts.last
       
        mail to: @user.email, subject: "Your post created #{@post.title}"
       
    end
end

Two ways solve this kind of errors:

1. Above case replace ActionMailer::Base from the PostCreate to ApplicationMailer
2. Add default mailer hash to PostCreate file.