If you have ever tried to send emails from your dedicated server in the cloud to either a mailing list or to individual users of your site, you would know that it is not as simple as it sounds. Depending upon the reputation of the IP address asigned to your server, many large email providers might block your emails - even though you have a perfectly legitimate reason to send this email, and your company has never spammed anyone. The solution we implemented was subscribing to the excellent Mandrill transactional email server from https://mandrillapp.com/ and sending all our emails via them. The problem then is how to makes sure all your emails as routed (relayed) through them? For your Drupal emails, you can use the Mandrill module, but that covers only Drupal (and has other issues). So what we really did was route emails to Mandrill at SMTP MTA (Mail Transport Agent) configuration level itself. The rest of the article describes how.
SpinSpire has special expertise and long track record on Drupal-based CMS, portals and custom applications. We have delivered high-profile Drupal projects for large companies.