new emails going to recipients’ Junk/SPAM folder

A couple friends who have successfully sent me many emails in the past are now going to my SPAM folder.  There are some similarities in both cases.  Both use Windows Live Mail 2012 (WLM) as their email program.  Both uses different internet service providers (ISP) than their email address domain.

One friend (Windows 7) recently switched ISP from Shaw to Telus.  She has kept her Shaw email address.  If she send me an email from WLM, it goes to my SPAM folder.  If she sends me an email from Shaw webmail, it arrives in my Inbox.  Prior to switching ISP, her emails from WLM would arrive in my Inbox.

Another friend (Windows 8.1) uses Shaw as his ISP, but has a Telus email address.  He also uses WLM as his email program.  His emails are now going to my SPAM folder.

I've gone into my Gmail SPAM folder and marked the emails from these two friends as "Not SPAM", but that didn't seem to help.

A third friend also uses Shaw as his ISP, but has a Telus email address.  He use Microsoft Outlook 2003 and his emails go to my Inbox.

So the issue seems to be when the ISP does not match the email address domain AND the email program is WLM.

I'd like to resolve this issue without having to install a different email program on the two friends' computers.

Can someone help me?