Can anyone shed any light as to why I often receive emails not addessed to
me.

The addresses used are similar but not the same and I would like to stop
this from happening. They are inevitably from spammers but I did a test
today and sent an email from an alternative account to one of the false
addresses recently used to send mail to my inbox and lo and behold - it
worked. How do I block the use of similar adresses so I only receive mail
sent to my proper email address? Any help gratefully received.
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Puzzled but determined to get there.