Hi Ken, thanks for your post! It looks to be more like an email provider issue, as when I click the link it opens up in Apple Mail with no trouble. This is absolutely still something we will investigate though, as I have confirmed the link is set up correctly. 

Is that Gmail where the address is failing to populate or a different email provider? Let me know so we can get this fixed

yes - in gmail it fails to complete the "To" field by clicking the link as shown in the image 

Thanks for specifying! Our team will take a look! It appears that we have what we need to investigate, but if we need more information we will contact you, and post the answer/resolution here. Thanks for letting us know about this!

Hello Ken, our team is still investigating this. We aren't able to reproduce the error ourselves (which is a good thing for your client, as this means it isn't affecting all Gmail users). Our team is reaching out to you directly to resolve this for you. In the meantime it does appear that this campaign is working normally for most users!

this issue now seems to be resolved - client sent an newsletter out today and all of the email links worked as intended 

That's great to hear! Glad that the user is able to use campaigns successfully! Thanks and please post again if you or the client run into anything else!