Outpost is a tool for managing email conversations between your team and your customers. It's not designed to be a mass-marketing or email newsletter tool.
There are limits to how many messages can be sent from Outpost each day, and these limits are set by your source email provider. A free Gmail account, for example, can send up to 500 messages per day. Check with your email provider to find out what limit it sets.
Email addresses created in Outpost have a limit of 100 messages per minute and 1000 messages per hour.
Note: cc and bcc recipients are included in your daily email limit. So an email sent to five recipients counts as five emails sent.
Note: The maximum number of recipients any message, reply, or forward sent from Outpost can have is 500.
There is no limit to the number of incoming messages you can receive per day in your Outpost account.