An example of the point made by davido and SuicideJunkie. Note that in the first print statement, which is not preceded by any successful match, the output is as you expect.

>perl -wMstrict -lE
"my $email = 'someuser@example.com';
 $email =~ /(.*) (<.*>)/;
 say qq{A: 1='$1' 2='$2'};
 ;;
 $email =~ /([^@]+\z)/;
 say qq{B: 1='$1' 2='$2'};
 ;;
 $email =~ /(.*) (<.*>)/;
 say qq{C: 1='$1' 2='$2'};
"
Use of uninitialized value $1 in concatenation (.) or string at -e lin
+e 1.
Use of uninitialized value $2 in concatenation (.) or string at -e lin
+e 1.
A: 1='' 2=''
Use of uninitialized value $2 in concatenation (.) or string at -e lin
+e 1.
B: 1='example.com' 2=''
Use of uninitialized value $2 in concatenation (.) or string at -e lin
+e 1.
C: 1='example.com' 2=''
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