Previously, I have added post on send email from application via postmark. [Check Here..][1] Now will see how to send attachment with email. In rails, action-mailer provides an easy way to add attachment file as attachments['filename.jpg'] = File.read('/path/to/filename.jpg') Links: [rails-guide-on-attchments(send attachments with email)][2] , [rails-attachments][3] Sending attachments via Postmark-api require "open-uri" def send_refer_pt_request(params, attachment) # attachment -> url of file saved on S3 if attachment.present? mime_type = MIME::Types.type_for(attachment).first url_data = open(attachment).read() attachments["#{attachment.split('/').last}"] = { mime_type: