Email - Outlook 365. When sending some emails, getting message from Avast Omni -
Malicious website blocked! We've saved Home from visiting a potentially dangerous site, smtp.xxxxxx.net, on their Windows Desktop PC.
Does not happen with all emails. Not finding any consistency for when it appears, e.g., sometimes happens with replies, sometimes happens with emails containing attachments, etc. but other times those types of emails do not give warning. Appears emails are successfully sent.
Any ideas as to why this message is appearing, if it is something to be concerned about, and how can it be fixed