The following section of mailto: code wasn’t working on the default Android email client and Gmail client.

<div class="panel-body">
Please contact the <a href="mailto:it.helpline@random.com?Subject=No%20Tiles%20within%20Application&amp;Body=Please%20could%20you%20check%20my%20account%20@(Model.LoggedInUser.Id)%0D%0A%0D%0AMany%20Thanks" target="_top">IT Helpline</a></div>

The reason is down to a simple issue ?Subject and &Body both started with capital letters, replace these to be lowercase ?subject and &body and the following code works across all clients on all platforms.

<div class="panel-body">
Please contact the <a href="mailto:it.helpline@random.com?subject=No%20Tiles%20within%20Application&amp;body=Please%20could%20you%20check%20my%20account%20@(Model.LoggedInUser.Id)%0D%0A%0D%0AMany%20Thanks" target="_top">IT Helpline</a></div>

I’ve tested on :

Android : Default mail, Gmail, Nine

iOS : Safari, Gmail

Windows : Outlook, Gmail