Issues with outgoing hotmail emails through Outlook for Mac

Hi - 

I am using a Mac (OS X Yosemite - version 10.10.5).  I use Microsoft Outlook for Mac for email and my primary email address is a hotmail account. 

I can normally send and receive my hotmail emails through outlook, but sometimes when I log on to different wi-fi networks (all private, password protected wi-fi networks, not free public networks), my emails do not send through outlook.  This happens on some wi-fi networks and not others and I can't seem to figure out why, even thought I have not changed the settings.  

I have recently moved and am using a new wi-fi and I cannot send emails through outlook.  

My incoming server is imap-mail.outlook.com and my outgoing server is smtp-mail.outlook.com.  

Does anyone have any ideas on how I can resolve this issue?  

Thank you,