He was detained yesterday under Section 41 of the Terrorism Act and taken to Musgrave Serious Crime Suite for questioning.
The device went inside a postal package inside the Co Down base which is also home to MI5 in Northern Ireland.
The attack was then part of a wider postal bomb campaign by dissident republicans.
Police say this morning that the man has now been released “unconditionally”.
Enquiries are continuing into tracing those behind the bombing campaign.