As Josh suggests, you should make mailto: links as generic as possible to maximize the chance of it actually functioning for a given lead. I would add both
mktNoTrack and
mktNoTok to such links.
mktNoTrack means you no longer rely on a browser bouncing from a web page (Marketo's click tracking page) back to the user's preferred mail app, but rather stay within the mail app in which the user is reading the message, which is by extension the preferred mail app. By counterexample, if the system's default mail app is Outlook, a mailto: link that bounces off a click tracking page will typically open Outlook -- even if the user read the message in GMail.
mktNoTok means your mailto: URLs look as non-dangerous as possible to mail apps. The spec for mailto: specifically says, "
Only the Subject, Keywords, and Body headers are believed to be both safe and useful." When Marketo adds its token, the final URL becomes something like mailto:someone@example.com?mkt_tok=aabbcc. Technically this means you are asking the mail app to set the unsafe mail header `mkt_tok` to 'aabbcc.' A mail app is free to see that attempt as malicious and never bring up the new message window. By simplifying the link to just mailto:someone@example.com, you stay within boundaries.Edit: here are two examples of what your leads experience if you don't include mktNoTrack and they are exclusively webmail users (they haven't configured a local mail app). It ain't pretty. Windows 8:
http://app.crossbrowsertesting.com/public/i75b45d927357249/livetests/2584450/videos/z0d245b96ed9a303...Mac:
http://app.crossbrowsertesting.com/public/i75b45d927357249/livetests/2584460/videos/zf9e3897cd2c9ddc...