How can I create a suppression list in Market so that certain contacts only receive specific emails?

Exclusion Smart List

- Filter: Email Address is "certaincontact1@email.com, certaincontact2@email.com"

In the Smart Campaign Smart List

- Filter: Member of Smart List in Exclusion Smart List

OR

In The Smart Campaign Flow Action

- Send Email

   - Choice 1: If Member of Smart List in Exclusion Smart List

   - Send Email A

   - Choice 2: Default

   - Send Email B

For a generic suppression list you need to build asmart lists in the Lead Database using the appropriate filters for your system,

I would start with these filters

____________

Unsubscribed

This is used on the standard unsubscribe page. If a lead checks this box, or clicks the unsubscribe link in an email, they will no longer receive marketing emails. They will, however, receive operational emails.

Marketing Suspended

This field is set by the user for placing leads on a temporary unsubscribe. Leads can only attain this status if they are manually changed, or a change data value flow step is utilized.

Blacklisted

Use this for competitors. They will receive neither Operational nor Marketing emails. They get nothing!

Email invalid

A mail server has told Marketo that the lead's email can't be delivered (for example hard bounces)

______________

and be sure to include a filter in every email campaign that says:
Member of Smart List NOT IN Suppression

Another option is to define Segments, so that your audiences are associated to them, then use that segment as a filter for inclusion or exclusion.

I generally like this as it is associates them by criteria and you don't have to continually query as you would a smartlist (in essence it is built in)