Mail not detecting blocked senders in emsil

I had a consistent sender that kept vetting messages in my inbox even though the sender was in my blocked list.

I then noticed that the sender had changed their address by making the initial letter upper case.

I deleted their original address from my blocked list and entered the new address - the ONLY difference being the use of the capital letter. Their messages are now recognised and filtered out into spam.

conclusion: mail is not recognising email addresses where capitalisation is used to prevent blocking.