[Exim] Another newbie question, exim 4 and local_part_suffix

I am trying to setup TMDA to work woth Exim 4. I added to userforward,
maildrop:, and localuser:

local_part_suffix = -*     # or "+*" if you prefer "user+suffix" addresses
local_part_suffix_optional

However if I sent an email to sean-dated-1015467965.fb7cd0@??? it
is returned to the sender as unroutable. I know I am missing something
but cannot work out what?

All suggestions welcome

Sean

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