Sorting Objects in an array by object properties

Hello list, I have an array which holds some objects. Each object represent elements from an email header in a given mailbox. Each object has properties like "from", "sendtime", "subject" etc. I want to sort the order of the objects in the array by their attribute "sendtime" in order to get a list of email header sorted by their arrival time. Has anyone an idea how to solve this? I tried various of the array sorting functions but without success. Thanks in advance Reto PS: The array has the following structure: Array ( [0] => mail_Header Object ( [id] => 1 [pid] => 1 [read] => r [flagged] => n [from] => reto@nerdbude.de [subject] => Re: [ugffm] TYPO3 anybody ? [sendtime] => 2005.05.17 - 18:27:25 ) [1] => mail_Header Object ( [id] => 2 [pid] => 1 [read] => r [flagged] => n [from] => reto@nerdbude.de [subject] => Re: [ugffm] website [sendtime] => 2005.05.17 - 19:13:26 ) .... )