... there are no GT or LT symbols in OP's sample
    my $email = 'someuser@example.com'
hence, dot star swallows all, in the relevant example.

If the relevant example is
    my $email = 'someuser@example.com'
    $email =~ /(.*) (<.*>)/;
    say "1='$1' 2='$2'";
from the OP, then dot star – i.e., (.*) – swallows nothing at all. The  '<' and  '>' characters are required to match, therefore there is no match, no swallowing, no capturing, nuttin'. As pointed out elsewhere, not even $1, $2, etc., are altered. In fact, because the first  (.*) capture group is followed by a required  ' ' (space), the angle brackets don't even figure in:  .* will initially grab everything, then backtrack repeatedly to try to match a space; finding none, it will eventually give up everything it grabbed and announce its miserable failure, triggering overall match failure.

The problem is actually why do I get some capture if I had no previous successful match.

In case of "foo <bar>" I definitely should get two captures, but I have no clue why do I get a capture "bar.com" with "foo@bar.com" sample. Observed on v5.10.0 DEVEL34916

See perlre:

NOTE: Failed matches in Perl do not reset the match variables, which makes it easier to write code that tests for a series of more specific cases and remembers the best match.

$1 and $2 have their old values from a match somewhere else in your code.

Always guard use of $1 with an if statement to make sure it matched:

if( m/(.*) <(.*)>/ ) {
    print "Matched '$1' + '$2'";
} else {
    print "Did not match";
};
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