Should I ask a professor for the third time for a letter of recommendation? I contacted two professors six weeks before the deadline. One prof emailed me back immediately. The second one still hasn’t. It is due in 3 weeks. I emailed him last Friday asking him again if he would be willing to be a reference but still no response. I don’t have his phone number and he doesn’t work at the university. I really don’t want to annoy him, but should I email him again? I do have his gmail address (I’ve been emailing him from his work one). Usually he contacts me from his work one but I have received ones from his gmail account in the past. But I am afraid this would be frowned upon and looked on as being too invasive? I am really at a loss. I do have another reference, however, she is more a professional reference and I am not sure if that is allowed (the school isn’t getting back to me on this question). 

This question is not a duplicate. I am wondering if I should email the professor for a third time or if that would be considered inappropriate?
I was in a similar position as you a few months ago. 

Given the deadline, it matters that something rather than nothing is submitted before the deadline. Ask asking for extensions is an unreliable strategy. 

Send an email to your professor stipulating that you are concerned about the lack of response (which you are) and inform the professor what your plans are (asking someone else). 

No need to ask why, be short and to the point. 


  Dear Professor X,
  
  It has been sometime since the last time we talked about you writing a
  letter of recommendation on my behalf. I am concerned that your
  silence is indicative of your unavailability to write a letter. I know
  you are busy and I understand your time constraints. 
  
  In the meantime I’ll be asking [you can choose to be specific or
  vague]. 
  
  Thank you for your time and consideration.
  
  Best regards,
  
  [Your Name]


Make sure the second letter writer is willing and able to submit in time.