Not recently, historically we did but it did not handle large spool directories very well. This was probably back on v14 so it may have improved. For this role Exim is your friend.

Thanks Nathan the issue there is I have zero Linux servers ad zero Linux knowledge :-)

Yes. We've used the Free version of the SM server to replace services like Mailchimp. It works well for one domain. You have challenges like you have with every domain (deliverability, SPF, domain keys, etc). It'll take some time to get trusted. I recommend giving yourself a 3-6 months of low volume transactional emailing to google and yahoo accounts to start to build up trust before any mass mailings. Even then, go slow and make sure your lists are double opt in etc. You need to of course secure the server, verify your TLS settings. So there is some overhead, but if you know your way around deliverability - we've had success going this route.

Yes, I do exactly this for custom applications I have created for clients. These applications generate many emails, ranging from ecommerce receipts to digital tickets to exam reminders.

The way I have configured it is to have a single subdomain for mail relays, and then I create one account for each client application. Each account then has a strong randomly generated password for SMTP authentication to the mail server. For instance, client@relay.host.com. I've found that this gives me a lot of flexibility in configuration and I can easily determine if one of the accounts is being abused. I can get reports of email volume per client as well. I don't know what kind of volume you are looking for, but I do hundreds of thousands of emails per month.

Michael's point about deliverablity is right on. I do set up SPF and DKIM, but I have to be extremely proactive to monitor our server's reputation. We do occasionally have problems being blacklisted, despite our emails being legitimate and not marketing-related. It seems that due to the volume of emails we send, even a small number of reports triggers listings, so be prepared to fight those battles with Microsoft, Comcast, Yahoo, etc. And, I have to think that some people just click the spam button (instead of the delete button) by mistake, not realizing that it will wreak havoc for email system admins for the next week. Sign up for their feedback loops and monitor any reports. Check out www.senderscore.org.

The other problem I face is limiting downtime while updating the email server software or operating system. I find that to be annoying. Most applications that send email don't have a backup SMTP connection to try, and most don't use a queue to store or re-try mail. So, if customers are making purchases during the time we're updating the software, their email receipt won't get sent. (In newer application we are writing, we are trying to address this by making each email into a task, and then retry the task if sending it fails.)

You could look at SendGrid (Twilio) as an alternative. I use Twilio for SMS notifications and like their service a great deal.

Hi Ben,

Great reply, thank you. sounds like the plan as my mandrill bill just keeps climbing especially since lock down and online traffic has rocketed!

We run a bulk transactional mail service using smartermail and it works well.

We have smartermail enterprise setup to handle authentication and tracking of all emails for accounting purposes, and it then sends the mail onto two free smartermail gateway servers which handle the delivery of emails.

The service works well 

Question - To lock it down fully, I plan to simply only open port 26 as an alternative SMTP port and only allow my server IPs access to that port on the firewall. Then keep the rest closed as its only EVER going to be used for sending out email. Or do I need to also open any other ports and make them public or locked down to IP?

You would need to have port 25 open for bounces, and sender verify checks.