Doing a "mail merge" from Microsoft Office to send out an individualized email I have an Excel spreadsheet with the grades of my students. Every so often I'd like to email out their current grades, one email per student, that will only include their last three homework grades or so.

Ideally I'd use Thunderbird to email it out but that might be trouble. Mail.app could also work, or Outlook in a pinch.

I've tried Word's Mail Merge and got all the way to the sixth step but the "Generate e-mail messages" option there is always greyed out, whatever I seem to be trying.

I'd also be happy with another solution, like using LibreOffice or exporting as text and using some command line tool to email it out but so far I haven't been able to emailing anything via mailx...
In the end, staying within the Microsoft Office environment is probably the easiest answer. Sorry for not having researched that more thoroughly before asking the question.

"Generate e-mail messages" in the last step was greyed out because Microsoft Outlook was not the default email application. So to make it work:


(Temporarily) Make MS Outlook the default email application: This is an option within the Mail.app preferences.
Go through the usual mail merge steps. Note that the email-address does not need to be in the Word message, but I would recommend to have it as a field in the Excel sheet.
In the last step the "generate e-mail messages" option should not be greyed out anymore. Select it.
A small window pops open. Among other options (Subject, for example) the field containing the email address can be chosen here. 
The format can be chosen as "Text", "HTML" and "Attachment". When sending as text, all me line breaks would disappear, so I ended up sending as HTML, even though I very much prefer "text"...
Done.
(7. Don't forget to undo your choice of default email app, if you normally use another one.)