A few points to mention: “double opt-in” will soon likely be a legality, with GDPR coming into force. Make sure your data is clean and engaged. That will boost your opens and CTRs too!

And the issue with saying Tuesday is a good day to send, is that everyone then sends on Tuesday and it becomes too busy. Like you say, just test when is best for your readers, that’s always the best way to optimise opens and click-through rates – TEST.

Furthering Kevin’s preheader text; this will take into account the first bit of text in your email. If you make this match your background colour you can hide the preheader from your main content – letting you use the Subject Line and preheader as promotions of your main message.

Great to hear proper names for images is helping Abby. Alongside mobile opens – make sure you’re not using too many images! The more images, the longer the load time, and that can be quite annoying when reading an email that takes some time to render.

And finally. Know your audience! Unicode emojis can be inserted into subject lines, if you’re reaching out to a millenials list consider saying more with the language they use…but tread carefully, of course.