Click activity

Yes.

Do not rely on Opens. Not every email viewer auto downloads images to mark the open.

Thanks Josh.  I appreciate it.

So you mean to say that Marketo cannot track the open activity in some cases ( depending on the email client's  auto download image settings)
Does that mean that if a lead has clicked activity, it automatically suggests email open although the lead may not show under open ?

Also if a lead does not click on an email and just open an email, is there a possibilty that the lead open activity might not be tracked ?
 

@Sarin N If a lead has Clicked Email activity, that means they've clicked a link in the email.  Therefore it always implies a human action akin to "opening" (or "reading"), even if they don't have images enabled.

And yes, if a user merely opens an email, even if they read it thoroughly, without images you will not see the Open activity.

Thanks Sanford.. Got it !