Emailing event participants - using 'send email' versus 'civimail'
I think I see what is happing.

When you select your  Participants (from Find participants) you only have an option for 


Email send now (50 or less)


When you select your Participants as Contacts (from Adv Search) you should have an option for 


Email schedule/send via CiviMail
Email send now (50 or less)


So, I think you can get what you want by searching for Contacts who were at your Event, and using that option, rather than searching via Find Participants.

NB iirc you need to have an existing CiviMail group that you use as part of this process, but it doesn't result in your participants being added to it. That said, I am not certain if all the bounce etc happens for these 'tack on' contacts but expect it would.

NB what the Action is called changes between versions so yours may be different if not 4.7.x.

READ MORE: instructions are at https://docs.civicrm.org/user/en/stable/email/mass-mailings-using-civimail/

starting with "If you are basing your mailing on search results, perform your search (for example, using Search > Advanced Search) and then choose Email - Schedule/Send via CiviMail from the Actions drop down. "