It is hard to tell what

@{$message->{headers}}
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contains because you did not enclose the output in <code/> tags.

In particular, it is not clear that the "From:" line starts at a newline boundary.

If it does, the correct way to capture the content is:

my ($from_address) = grep /^From:\s/i, @{$message->{headers}}; 
  #^             ^  Parens added to create list context, to get CONTEN
+T rather than COUNT
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It would also help if you identified what variable was dumped using Data::Dumper, and had that formatted better , using <code> tags.