In my web page I make an Ajax request to a WCF service. If the service throws an error then that is passed back in the JSON. The JavaScript error handler then reveals a hidden div with a mailto URL prepopulated with my details so that team members (this is a small internal app) can send me the error including the stack trace. Here's an example resulting URL from a test run:
mailto:[email protected]?subject=potential%20seed%20save%20failed&body=Potential%20seed%20URL%20=%20unknown%0DResponse%20%3A%20%7B%22ExceptionDetail%22%3A%7B%22HelpLink%22%3Anull%2C%22InnerException%22%3Anull%2C%22Message%22%3A%22testing%22%2C%22StackTrace%22%3A%22%20%20%20at%20SavePotentialSeedSearches.WCFService.StorePotentialSeed(String%20url%2C%20String%20name)%20in%20C%3A%5C%5CTFS%5C%5CProjects%5C%5CSeeds%5C%5CPreliminaries%5C%5CSavePotentialSeedSearches%5C%5CWCFService.svc.cs%3Aline%2021%5Cu000d%5Cu000a%20%20%20at%20SyncInvokeStorePotentialSeed(Object%20%2C%20Object%5B%5D%20%2C%20Object%5B%5D%20)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object%20instance%2C%20Object%5B%5D%20inputs%2C%20Object%5B%5D%26%20outputs)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean%20isOperationContextSet)%22%2C%22Type%22%3A%22System.ArgumentException%22%7D%2C%22ExceptionType%22%3A%22System.ArgumentException%22%2C%22Message%22%3A%22testing%22%2C%22StackTrace%22%3A%22%20%20%20at%20SavePotentialSeedSearches.WCFService.StorePotentialSeed(String%20url%2C%20String%20name)%20in%20C%3A%5C%5CTFS%5C%5CProjects%5C%5CSeeds%5C%5CPreliminaries%5C%5CSavePotentialSeedSearches%5C%5CWCFService.svc.cs%3Aline%2021%5Cu000d%5Cu000a%20%20%20at%20SyncInvokeStorePotentialSeed(Object%20%2C%20Object%5B%5D%20%2C%20Object%5B%5D%20)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.SyncMethodInvoker.Invoke(Object%20instance%2C%20Object%5B%5D%20inputs%2C%20Object%5B%5D%26%20outputs)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage31(MessageRpc%26%20rpc)%5Cu000d%5Cu000a%20%20%20at%20System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean%20isOperationContextSet)%22%7D
That's 2354 characters long.
Other answers suggest that URLs above 2000 characters are a bad idea as some browsers may struggle with them. But are mailto URLs parsed in any way by the browser or are they handed immediately on to the default mail tool? If they are handed on, does anyone have data on the length of mailto URLs that various mail tool (and in particular Outlook) can handle?