Conetix places limits on the amount of email which can be sent through any of the managed services (such as shared hosting and managed email). These limits are set high enough to allow normal business usage but will limit email which is considered to be "bulk" or spam. This is to prevent the blacklisting of these services, which will affect the sending of your normal email as well.
Any direct email marketing (such as newsletters, promotions etc) should be sent through a managed, transactional mail service which will provide greater control and reporting. Systems such as MailChimp will integrate the mandatory unsubscribe option and also provide detailed reporting such as who opened the email and how many failed to deliver.
Here's what we recommend:
MailChimp is en easy to use email marking service, which provides cost effective, easy to use system.
Bulk SMTP Sending
If you have an existing system or use a billing mailout, SparkPost is a great bulk email platform. Up to 100,000 emails are allowed per month for free and they have both an extensive API as well as standard SMTP interface.
Mailjet incorporates both traditional email marketing systems as well as allowing SMTP relay. With an easy to use interface and cost effective plans for sending email (free for up to 6,000 a month) it's a good first option to use.