Can someone who unsubscribed still receive future emails?

Bentacular - I would recommend logging a customer support ticket at this point, and they'll be happy to troubleshoot this for you.

@ Bentacular: as far as I know, all complaints we had received were always justified. Either the lead thought he was unsubscribed but wasn't, or he had received an operational email, or he had 2 different email addresses, or (as Kenneth E mentioned) he is receiving emails from an alias/re-direct from a former colleague to his mailbox.

When I cannot find an obvious reason, what I usually do is check with the leads which email address they think they have unsubscribed to and ask them if they are receiving our newsletters under other addresses.

Ben, 

Definitely ask customer support at this stage. It's probably a duplicate error between Contact and Lead and different leads are qualifying and only 1 has unsubscribed. I thought they had fixed that issue.
 

If the person has multiple email addresses (jhill, josh.hill, jdhill @samecompany.com) only one will be unsubscribed.

If someone fills out a form without an opt in box, they should NOT be automatically opted in (or back in).

It's probably a duplicate error between Contact and Lead and different leads are qualifying and only 1 has unsubscribed.
@ Josh Hill :You are talking about Contact & Lead in SFDC right? because we only have leads in MKTO or am I mistaken?

I thought they had fixed that issue.
Are you saying that if a contact with multiple email addresses ask to be unsubscribed all their related email addresses should be unsubscribed? (lf MKTO was working properly). What about leads who let's say have multiple email addresses and only want to unsubscribe one that they are no longer using?

Thank you everyone for your comments!

Apparently the unsubscribed lead I was looking was actually NOT sent an email but the program was changing the status to --> SENT. No actual emails were sent.

Here's another thing I just learned. Apparently, even if a lead is already unsubscribed, it still qualifies for campaigns and mucks up your sent numbers. It's imperative that you add Unsubscribe = False as part of your smart list filters to exclude unsubscribes right off the bat. I thought it would be logical for Marketo to just exclude them since they will never receive the email anyway. Go figure.

Ben - I just did a test to myself, wherein I was unsubscribed, and I created a campaign to send myself an e-mail. After the campaign ran, I looked through the results of the campaign, and Marketo reflects that the e-mail was not sent. The results also did not say that 1 e-mail was sent (which is what you're implying), so I don't think Marketo reflects the Unsubscribes in the Sent numbers/stats. This seems correct, and based on the test I did, I don't think you need to include the Unsubscribed=True filter in campaigns to reflect the correct stats.

That's true as long as in your FLOW you don't have a step called Change Program Status ---> SENT

Hey Ben,

One common practice in this particular case it to make your Change Program Status> Sent flow step conditional.  To do this you use the Add Choice option on the flow step to have the "If Was Sent Email is [Your Email] Change Program Status > Sent" and then have the default choice be do nothing.  This will ensure that any leads that were not actually sent the email do not have their status changed.