I like to use wheregoes.com to probe links. I'm surprised at how many redirects some of them have. I get that an ad link might go through an ad channel, but clicking one non-spam link from a reputable company can plant cookies from a whole bunch of websites.
Send me plain text email.
Add attachments that I can scan for issues before I open them.
If you send me links, I will be very wary of visiting them outside a sandboxed tab. I will not 'click through' from the email client.