do not use sendgrid URLs in email that trigger scam detection
The sendgrid URLs you use cause scam detection to trigger on Thunderbird due to the fact the display URL and the actual URL mismatch.
The linked URL is "http://u10487.sendgrid.org/wf/click?upn=n7wRGsZfdIkZD7pP5rH0pBeid .... ", but the display URL is http://www.playconclave.com/characters/xxxxx/play.
Why not just link directly to the characters/.../play URL, instead of via sendgrid?
You'll probably trigger scam detection anytime the link text and the link destination are both URLs but go to different places, as that's a common way to make people think they're going one place and taking them to another similar-looking site.
AdminDerek (Manager, 10x10 Room) commented
Thanks for the heads-up about Thunderbird. We use SendGrid so that we can tell whether people are clicking on the links in our emails; it helps us know whether we're doing a good job of keeping them useful. We'll look into alternatives.