We currently have our own in-house email marketing software for our newsletters, and were using SQL server's SMTP agent to send emails through our local SMTP server (IIS) and then onto our ISP's SMTP Relay.
The SQL Server was involved because the email addresses of the recipients are stored in the database and because it takes the content of the newsletters and we use .net to construct the emails for delivery.
About 1 month ago our ISP got the impression we were sending spam (our email volume is approx 20k a day) and blocked the SMTP relay. After much debate with them, we've given up with them, but realised that they came to this conclusion due to the high volume of NDRs.
We've solved the problem with the NDRs but going back to the ISP SMTP relay isnt currently an option.
Using IIS as a direct SMTP server is not ideal because we cant implement systems that will help us to deal with bypassing spam filters since we need to implement DKIM and SPF and its not so easy on IIS.
We tried using our shared hosting accounts with just standard SMTP hosting to send out our emails from the SQL server but the email limit is set to 300/hr which isnt high enough, and currently using something like SendGrid is just too costly at this volume since we dont profit from the newsletters.
While i have previous experience with Exchange 2003 and 2007 i just find the maintenance and hardware requirements to be quite involved at times and am looking for a minimal but flexible and capable solution for an SMTP that can support DKIM and SPF.
I have been considering something like QPSMTPD or the Node.js port; Haraka.
Does anyone here have any experience with the above and how quick and easy are either to implement, maintain and extend?
What about DKIM and SPF support?
What about dealing with such a high volume and required speed?
Am i likely still to come across spam filtering issues and problems with my ISP?
Does anyone have any insight they can share on this matter?