Hi Crispin,
I am using mojoPortal to send my newsletter but I have configured it to use Elastic Mail by smtp configuration for both the newsletter and for the forums because we send a great deal of email. See the article Sending Bulk Email for information about to configure different smtp settings for newsletter and/or forums.
You have it backwards on the posts about GoDaddy, they only support their own smtp which is very limited in the amount of mail you can send, they don't allow you to relay through other smtp server such as those provided by Elastic Mail. That is why someone in another post was asking about implementing the alternate way of using Elastic Mail by REST web services instead of direct smtp.
The only reason I started using Elastic Mail is because I don't currently have a strong mail server infrastructure, previously I was using my Yahoo business email account to send email and a lot of it was getting flagged as spam, so switching to Elastic Mail made things work a lot better for me. But if your mail is working fine I would not see a reason to change it. One day I may setup a good mail server and stop using Elastic Mail because I've been spending about $50/month since we send a lot of mail, but the good thing is that the price per email goes down after you reach certain thresholds, like after we have sent a total of 100,000 emails our rate per email dropped a good bit so now it costs a little less.
Best,
Joe