We have been using the SparkPost extension (civi desk) about a month and it is sending emails fine. However, it may not be processing bounces completely and/or I do not understand how it works. If we get a hard bounce should the contact's email address be placed "On Hold"? I am getting bounces documented in the CiviMail Reports for a mailing. The only bounce type I see in these reports is "Syntax". These emails are not getting placed "On Hold". Should they be placed on hold automatically?
There's a forum discussion here which I think helps towards the answer. If you look at the table civicrm_mailing_bounce_type there's a threshold of 3 for bounce type 'Syntax'. I just encountered a bounce for type 'Host' that didn't place the email address on hold, so was also concerned as to why. The answer is in this table.