My primary email address is in the format firstname.lastname@example.org.
Incoming and outgoing emails have worked almost flawlessly for years.
Outgoing emails are still fine and so are incoming emails provided they are original messages addressed directly to me.
However, three times in the past few weeks attempts by contacts of mine to forward an email to me or reply to an email of mine have failed and the senders received bounce back messages with the error '552 Spam Message Rejected'.
In one case a friend about to visit me tried to forward me her travel details from a train company.
In another, my wife (who uses Gmail) twice tried to forward me a legitimate email she'd received from Sainsburys supermarket.
In the third case, a friend who runs a computer repair business tried to reply to a business-related email from me and got the same result..
I attach the headers from the bounce back emails received by the senders in cases 2 and 3.