You may want to use an external SMTP server (such as those provided by Google or Mandrill) to send e-mail messages from your A2 Hosting account.
However, if you have one of the following hosting packages, you cannot use external SMTP servers to send e-mail:
For these hosting packages, you must use A2 Hosting servers to send e-mail messages. A2 Hosting enforces this restriction to help prevent outgoing spam from our servers. It only takes one user sending spam from a shared server to negatively impact e-mail for all of that server's users.
All other hosting packages are not subject to this restriction, so you can freely send e-mail messages through external SMTP servers. These hosting packages include: