You need to build proper Perl code and a proper shell command.

use String::ShellQuote qw( shell_quote );

sub perl_quote { qq{"\Q$_[0]\E"} }
 
my $email_lit = perl_quote( $email );

my @cmd = (
   "perl",
   "-MDigest::SHA=sha256_hex",
   "-e", "print sha256_hex( $email_lit )",
   $email,
);

my $cmd = shell_quote( @cmd );

my $email_SHA256 = qx($cmd);
die "Can't spawn child: $!\n" if $? == -1;
die "Child killed by signal ".( $? & 0x7F )."\n" ) if $? & 0x7F;
die "Child exited with error ".( $? >> 8 )."\n" ) if $? >> 8;
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If we pass the address as an argument, we don't have to build any Perl code.

use String::ShellQuote qw( shell_quote );

my @cmd = (
   "perl",
   "-MDigest::SHA=sha256_hex",
   "-e", 'print sha256_hex( $ARGV[0] )',
   $email,
);

my $cmd = shell_quote( @cmd );

my $email_SHA256 = qx($cmd);
die "Can't spawn child: $!\n" if $? == -1;
die "Child killed by signal ".( $? & 0x7F )."\n" ) if $? & 0x7F;
die "Child exited with error ".( $? >> 8 )."\n" ) if $? >> 8;
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Better yet, we can avoid the shell, and avoiding building a shell command.

use IPC::System::Simple qw( capturex );

my @cmd = (
   "perl",
   "-MDigest::SHA=sha256_hex",
   "-e", 'print sha256_hex( $ARGV[0] )',
   $email,
);

my $email_SHA256 = capturex( @cmd );
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(capturex already provides error handling.)

As already pointed out, this is silly, though. Because you simply need:

use Digest::SHA qw( sha256_hex );

my $email_SHA256 = sha256_hex( $email );
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