Play custom audio alert for certain incoming mail I would like my Mac to play a sound when certain email arrives. For example if the subject contains "xyz", play "mycustomsound.mp3".

Any easy way to do this?
Assuming your using Mail.app, add a mail rule.

Go to Mail -> Preferences -> Rules. Add a rule based on your criteria (Subject Contains | Is Equal To | Starts with "xyz").

Under "Perform the following action" select "Play sound". You can choose a preset sound or select "Add/Remove" to set your own custom sound.