Tldr

This gem uses both Mandrill API and ActionMailer to send email.

Setup

Add this to your .env

BASE_URL_FE=
DEFAULT_EMAIL_SENDER= 
USE_MANDRILL_MAILER= 
MANDRILL_SMTP_ADDRESS=
MANDRILL_SMTP_DOMAIN= 
MANDRILL_SMTP_PASSWORD= 
MANDRILL_SMTP_USERNAME= 
MANDRILL_SMTP_PORT= 
MANDRILL_SMTP_AUTO_TLS= 
MANDRILL_SMTP_TLS=

MAILER_SMTP_ADDRESS=
MAILER_SMTP_DOMAIN= 
MAILER_SMTP_PASSWORD= 
MAILER_SMTP_USERNAME= 
MAILER_SMTP_PORT= 
MAILER_SMTP_AUTO_TLS= 
MAILER_SMTP_TLS=

Add this to config/initializer/mailer.rb

ActionMailer::Base.delivery_method =: smtp

# change it to your helper class name
ActionMailer::Base.add_delivery_method: mandrill_mailer, MandrillMailer

# uncomment
if neccessary
smtp_settings = {
    address: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? ENV['MANDRILL_SMTP_ADDRESS'] : ENV["MAILER_SMTP_ADDRESS"],
    # authentication: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? 'plain' : nil,
    domain: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? ENV['MANDRILL_SMTP_DOMAIN'] : ENV["MAILER_SMTP_DOMAIN"],
    enable_starttls_auto: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? true : false,
    tls: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? true : false,
    # password: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? ENV['MANDRILL_SMTP_PASSWORD'] : ENV["MAILER_SMTP_PASSWORD"],
    port: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? ENV['MANDRILL_SMTP_PORT'] : ENV["MAILER_SMTP_PORT"],
    # user_name: ENV["USE_MANDRILL_MAILER"].to_i == 1 ? ENV['MANDRILL_SMTP_USERNAME'] : ENV["MAILER_SMTP_USERNAME"],
    # openssl_verify_mode: "none",
}

if ENV["USE_MANDRILL_MAILER"].to_i == 1
smtp_settings[: authentication] = 'plain'
smtp_settings[: password] = ENV['MANDRILL_SMTP_PASSWORD']
smtp_settings[: user_name] = ENV['MANDRILL_SMTP_USERNAME']
end

ActionMailer::Base.smtp_settings = smtp_settings

ActionMailer::Base.default_url_options = {
    : host => ENV["BASE_URL_FE"]
}
ActionMailer::Base.register_preview_interceptor(ActionMailer::InlinePreviewInterceptor)

# Don 't care if the mailer can't send.
ActionMailer::Base.raise_delivery_errors = true
ActionMailer::Base.perform_deliveries = true
ActionMailer::Base.perform_caching = false

MandrillMailer.configure do |config |
    config.api_key = ENV["MANDRILL_SMTP_PASSWORD"]
    config.deliver_later_queue_name =: default
end

# How to Use

Mandrill Example

require 'dcidev_mailer/mandrill'

class MandrillMailer
  class << self
    def send_email(customer: nil, email_template: nil, attachments: nil, description: nil)
        raise "invalid customer"if customer.nil?
        raise "invalid template" if email_template.nil ?
        begin
            response = ::DcidevMailer::Mandrill.send_email(
                subject: email_template.subject,
                html_body: MailerHelper.format_wording(email_template.wording, customer),
                header_url: email_template.header.try(: url),
                footer_url: email_template.footer.try(: url),
                to: customer.email,
                cc: nil,
                bcc: nil,
                from: ENV['DEFAULT_EMAIL_SENDER'],
                attachments: attachments,
                email_template_path: "mail/blast.html.erb"
                # specify template file location
            )
        rescue => e
            error_message = "[SEND EMAIL] " + e.try(: to_s)
        ensure
             EmailHistory.create(application: customer.application, template: email_template, status: response[0]["status"] == "sent" ? : sent:: failed, mail_provider_id: response[0]["_id"], form_cetak_attachment: attachments.present ? , error_message : response[0]["reject_reason"]) if response.present ?
             ApplicationHistory.log(description: error_message || description, application: customer.application)
      end
  end 
end

Action Mailer Example

require 'dcidev_mailer/rails_mailer'

class MortgageMailer  
    class << self  
        def email(customer: nil, template: nil, file_attachments: nil, description: nil)  
            begin  
                raise "invalid customer" if customer.nil?  
                raise "invalid template" if template.nil?  
                raise "email is empty" if customer.email.nil?  

                wording, _ = DcidevMailer.format_image_from_html(template.wording)  
                wording = MailerHelper.format_wording(wording,customer)  

                DcidevMailer::RailsMailer.email(  
                    html_body: wording,  
                    header_url: template.header.try(:url),  
                    footer_url: template.footer.try(:url),  
                    file_attachments: file_attachments,  
                    to: customer.email,  
                    cc: nil,
                    bcc: nil,
                    subject: template.subject,  
                    from: ENV['DEFAULT_EMAIL_SENDER'],  
                    template_path: "mail/blast.html.erb"  # specify template file location
                )  
            rescue => e  
                error_message = "[SEND EMAIL] " + e.try(:to_s)  
            ensure  
                EmailHistory.create(status: error_message.present? ? :failed : :sent, error_message: error_message, application: customer.application, template: template, form_cetak_attachment: file_attachments.present?)  
                ApplicationHistory.log(description: error_message || description, application: customer.application)  
            end  
        end 
    end  
end

Helpers

# convert all image URL in <img src="url"> to <img src="cid:xxxx">
DcidevMailer::format_image_from_html(html)

# format array of attachment files
DcidevMailer::format_attachments(attachments)

# format email header & footer url to be embedded to html body
# refer to class DcidevMailer::Mandrill or DcidevMailer::Rails to understand more of this method
DcidevMailer::format_header_footer(header_url: "", footer_url: "", locals: {}, images: {})