Mandrill is a transactional email service, the benefits of which include:

- Wrapping your emails in templates. With this, you can have your "lost password" and similar emails be branded properly AND include 10%-20% marketing material, like Amazon does. Very effective stuff as transactional emails have an open rate MANY times higher than marketing emails.
- Tracking emails sent from your site.
- Knowing what got delivered and what bounced.
- Having logs to see WHY something from your site bounced.
- Seeing what links people are clicking (even in plain-text emails, through link re-writing)
- Improved deliverability because that's all they do, deliver email, so they do it well.
- It's more like outsourcing your SMTP server than relying on their reputation for your email sending.
- You need to modify your DNS records to add SPF and DKIM records to "authorise" their servers for sending on your behalf.

I've saved me money on people cancelling accounts with me because they didn't receive replies to their support requests. I've also saved money on clients requesting refunds because they never got the email from the site saying their payment was received. And I've made money in renewals from people who otherwise would have not received their renewal reminders.

Mweb.co.za is a particular pain in the ass. I've had countless issues with emails from my site never being delivered to an @mweb.co.za address. Pretty serious stuff when you're trying to email people support replies, payment notifications and renewal reminders!

Having said all that, it's admittedly a service better suited for e-Commerce sites (like www.just1.co.za) than forums. (Still, I now use it on every site and have definitely noticed an improvement in activations of accounts, etc.)