Out of the box, both Magento 1 and 2 send email using PHP and sendmail. This means rather than sending your sales or order emails to customers via an existing mail service such as Mandrill or an Exchange server, the email goes out directly from your server at MageMojo.
While this works fine in most cases, we do recommend using an SMTP module or plugin for either version of Magento to improve deliverability. Especially for our high traffic stores. If you send out a lot of emails daily, you run the risk of getting your server here blocked by the major email providers such as Gmail or Hotmail due to volume. Sending out through dedicated services like Mandrill or Sendgrid, allow you to send high volumes without risk of blacklisting.
Magento 1 SMTP
Magento 2 SMTP
Currently, we do not have direct experience with a particular SMTP plugin for Magento 2. There are several available and even one specifically for Sendgrid. Two are listed below which are free, we cannot guarantee their reliability, however.