Research Director not responding to email - should I call him? I'm posting this question because normally he is a very punctual person, often responding within a matter of hours if our time zones match up. However, I sent an email last week and a follow-up one on Sunday, and he has yet to read it (according to my email-tracking software). 

I don't think his university has started break yet, so should I wait a little bit and leave a message? 

Edit: Question should not be considered a duplicate because I am inquiring as to whether I should call him now that email seems to be "exhausted" so to speak, but I'm not sure if calling is appropriate.
Before you call him, email the department receptionists and ask if the Research Director is around. It's possible he's on holiday, he's on bereavement leave or paternity leave, he's attending a conference, and so on. The department receptionists are likely to be more familiar with his schedule than most. If they say he's around, you can also ask them to pass a message to the Research Director.