Send Email vs Email bounce

If you are referring to the Activity Detail in the Activity Log, "Send Email" means that someone at your organization used Marketo to send out an email to the lead.  "Email Bounced" means that the email did not reach its intended recipient for a variety of reasons.  Some of those reasons may be temporary (e.g. server busy, mailbox full) and those are considered "soft bounces".  Other reasons may be permanent (e.g. SMTP 550 errors such as mailbox does not exist) and those are considered "hard bounces".  Marketo will change the value of the Invalid Email field to "True" if there is a hard bounce.

Thansk Elliott.  So send email just means that the email was sent but the server didn't receive a report whether it bounced or was successfuly delivered?

The Send Email activity that is logged is based solely on the email being sent by the Marketo email server.  After a Send Email activity is logged, a Email Delivered or Email Bounced activity will be logged as well, but this could occur hours later.  It is up to the recipient's email server to send a reply back to Marketo's email server and depending on how the recipient email server is configured and its load, it may take several hours to get the response back.

Yup they are 2 different things. Send email just means it was send but doesn't guarantee that it was delivered. Email bounced means it didn't make it in the inbox, but it might be temporary or permanent. 

Thank you both!