How do you overcome the issue of image blocking in emails?

Here's an easy fix.

Near the top of your newsletter, add the following line:

"If you are having trouble viewing this email, click here to read online." [Click here links to the online version.]

The main reason people used image blocking in the first place was because they had slow connections. A simple image could take several minutes to download. Couple that with metered access, and blocking images was a huge time and money saver.

The secondary reason for image blocking was security. It's possible to download malware rather than the promised image, although this is much more rare than it was in the old days.

Nowadays, it won't be a big issue. Just add the suggested line for the people for whom it is an issue. And don't forget to add alt text to the image so people can tell what they are supposed to be seeing.

As for whitelisting, unless your audience is savvy enough to know what that means, I'd keep it very simple. In your welcome email, simply ask them to add your sending address to their contacts or drag the email to the primary tab and drop it there.