Enhance Ruby net/smtp library to be never interrupted by errors while mail sending to multiple recipients.

Sometimes, when you are sending mail to multiple recipients, once there is at last 1 error in address of recipients, such as email address is not existed, or some recipients have blacklisted your mail address, the whole sending progress will be failed. No matter what your Ruby framework or Ruby gem you used.

Because this is a problem of Ruby baisc library net/smtp. In the SMTP class you can find this function rcptto_list which transfer recipient email addresses to Mail server one by one and deliver the mail data at last. Unfortunately, during the process, if any SMTP error raised by address transfering, the whole sending process will be halt at once. That is to say all the recipients will not receive the mail. Technically based on it's current logic, if the error is SMTPAuthenticationError, the email will be still sent, but it's not enough.

This patch is to fix this problem to keep mail be always sent and raise errors(if existed) at last.

BTW, some other languages' SMTP library, such as smtplib in Python, nodemailer in Nodejs are working without the problem. 😅

Add the gem to your Gemfile:

gem 'smtp-patch'

Install the gem with bundler:

bundle install

Once you are using this patch in your project, the mail will always be sent when you are sending a mail to multiple recipients. Meaningwhile, during the sending, if there are errors happened, the errors will not raise at once but raise after email sent out. You can catch the errors like below:

begin
  recipients = %w(jjlin@example.com jaychou@example.com)
  Mailer.test_email(recipients).deliver_now! # Rails Mailer example
rescue => e
  puts e.class #=> Net::SMTPErrors
  puts e.message #=> failed to deliver for {"jjlin@example.com"=>#<Net::SMTPFatalError: 554 RCPT (jjlin@example.com) dosn't exist>}.
  puts e.errors #=> { "jjlin@example.com" => #<Net::SMTPFatalError: 554 RCPT (jjlin@example.com) dosn't exist> }
end

Released under the MIT license. See LICENSE file for details.