On GitHub is a python script for doing mailmerge from the command line. It works great on OS X (see the link below). I found this much more powerful than the problematic Microsoft Office and App Store solutions to doing email merge. One of the great things about Email Stack is that it seems to handle Outlook's quirks quite nicely, and its ability to generate beautiful emails far outshines anything on the web.
To run the mailmerge, you need to have some familiarity with command line tools. I needed to install Python3 from python.org before I could install mailmerge. Once it is installed, follow the steps and templates carefully and you can easily use Email Stack HTML emails to create compelling emails. It took me a couple of trial and errors, since I was not completely familiar with the specifics of the email file format.
A couple of hints:
I love that you can run multiple tests with mailmerge, even before you are sending it out to the mail server. It took me some trial and error to make sure I had the correctly formatted content file, subject lines showing up where I wanted then, and preview text (the first text of a plain text file, and embedded in the HTML file) showing up properly.
Put your own name and test email FIRST into the .csv. mailmerge by default only runs the first entry, and you can run your tests multiple ways.
Preview your tests on multiple mail clients and devices. I found variances in how they each handled emails.
Email Stack can generate LONG lines of HTML with no line breaks. mailmerge does not do any processing of your HTML like, say, MailChimp might. I needed to break these long lines into shorter lines (put a newline between <> <>'s) to prevent artifacts or errors showing up in my emails.
I successfully used mailmerge with all types of image referencing: with referencing images warehoused elsewhere, publishing a RW project and then using the direct link to the published image, and using attachments. (more on that below)
Make sure you have the preview text set in the Slogan for the page. I manually edited the preview text in the plain text portion of the email.
I generated my .csv from Numbers exported spreadsheets. You of course could use Excel or (gasp) plain text editor.
I had no spaces in my header row entries - my guess is that macros wouldn't work with the spaces in the header row.
The Subject line in mailmerge's content file had to be entered manually - it is not pulled from the Email Stack code.
Embedding images
By embedding the images directly into an email, I don't need to rely on having the image somewhere on the web for your email to be fully rendered.
For embedding attached images directly into the mailmerge, I was unable to send both HTML and plaintext in the same email - I could only figure out how to do it with a pure HTML email.
I followed the template for setting up attachments in mailmerge, and then I used the referenced name in "warehouse" image mode in Email Stack. You won't be able to preview the image in RW, since the URL you use is only the exact name you used in "ATTACHMENT" in mailmerge. I set up my layout first by dragging images into the stack, and then when I was ready, I changed the image type to warehouse and used the URL of the attachment name.
Here's what the top of my content file looked like for embedding the attachment:
TO: {{Email1}}{% if Email2 %}, {{Email2}}{% endif %}
SUBJECT: You Are Invited to ...
FROM: Henry Flurry <[email protected]>
Content-Type: text/html
ATTACHMENT: invite.png
ATTACHMENT: andalusia.jpg
<!DOCTYPE html PUBLIC"-//W3C//DTD XHTML 1.0 In the warehouse URLs within the Email Stack Image, I put only "invite.png" and "andalusia.jpg". These were two image files in the same folder as my mailmerge source files. The <!DOCTYPE ... is the HTML pasted from Email Stack.
The mailmerge feature is fairly powerful. In the example above, I have a simple if statement to include the second email address if there is one. I was able to embed fields within the RW page so that the content was customized. I did not try embedding macro logic within the RW page - I'm not sure if any of the codes would be munged to make them HTML safe.
I'm popping this info out here because for years I'd been looking for a locally hosted solution that allowed flexible and beautiful output. I apologize in advance that I won't be able to address detailed questions on how to set things up - I am trying to meet many deadlines.
I hope this is helpful to others...