Undefined Method `smtpapi` for an instance of Mail::Message

[stephen-found]

System Information

• Ruby 3.3.5
• Rails 7.1.5.1
• Mac OS 15.5 (24F74)

Steps to Reproduce

• rails new mailer-test
• add gem to Gemfile gem "mail-x_smtpapi-ksr" and bundle install
• add random mailer under mailers

class RandomMailer < ApplicationMailer
  default from: 'notifications@example.com'
  
  def welcome_email(recipient)
    @recipient = recipient
    @url = 'http://example.com/login'
    
    # Set the SMTP API category to 'test'
    mail.smtpapi.category = 'test'
    
    mail(
      to: recipient,
      subject: 'Welcome to Our Application!'
    )
  end
end

• start rails console

mail = RandomMailer.welcome_email('test@example.com')
puts mail.to_s

app/mailers/random_mailer.rb:9:in welcome_email': undefined method smtpapi' for an instance of Mail::Message (NoMethodError)

This was experienced in a production app:

NoMethodError: undefined method `smtpapi' for an instance of Mail::Message
from /bundle/ruby/3.3.0/gems/mail-2.8.1/lib/mail/message.rb:1389:in `method_missing'

before testing on the new rails app. any info is greatly appreciated