Email to self Undeliverable

Mail
1

If an email to myself using eM Client (or have myself in the list of recipients),
I get a message back from Microsoft Outlook “Undeliverable” with "Remote Server returned ‘550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)’ " in the detail.

If I bypass eM Client, and send the same email direct using Microsoft Outlook, eM Client picks up the mail ok. Similarly if I send from gmail, eM client works ok.

So it looks like a problem on sending from eM Client - I am sure this used to work ok.

2

Problem is limited to eM Client -> MS Outlook. Have tried the same test with my Gmail account, and that works.
Have also tried deleting the Outlook account and setting it up again, but the problem comes back.

3

Has started working now, mail addressed to myself is being delivered.
I dont think its because of anything I did and suspect MS Outlook have made a change.