Windows 10. Office 365 Business Premium. Outlook 2013 syncing with Exchange online.
I have business dealings with a woman in Kolkata, India. She receives all my emails but when she sends to me they bounce. This started within the last month or so and I've been dealing with her for years without this problem. I've checked she's not on my blocked list. I've checked on https://www.spamhaus.org/
and found her domain is not blocked. I have 3 email addresses on the same domain but the same thing happens when she sends to any of them. I also have an imap/smtp personal account. The same thing happens when she sends to that address. When she uses her Hotmail account I do receive her emails. What's my next move please?