how could I pass this array of hashes "@imgs" to this module?

Normally, you'd pass a reference to it, i.e. \@imgs

email( {to=>$to, from => $email, ..., imgs => \@imgs} );
...

sub email {
    my ($vals) = @_;
    ...
    my $imgs = $vals->{ imgs } || [];
    ...
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Further on, you then just dereference it the usual way: @$imgs for the entire array, or $imgs->[0] for a single element (which would be a hashref in your particular case).

See also perlreftut and perlref.

P.S. you probably don't want to supply an empty hashref ({}) as defaults for things which are normally just scalars/strings, such as your

    my $to = $vals->{ to } || {};
    my $from = $vals->{ from } || {};
    my $subject = $vals->{ subject } || {};
    ...
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