$address =~ s/([^@>]+[@>][^,]+),s*/$1n/g;

$address ="mail1, local<mail1@mail.local>, mail2@mail.local, <mail3@mail.local>, mail4 local<mail4@mail.local>"

mail1, local<mail1@mail.local>
mail2@mail.local
<mail3@mail.local>
mail4, local<mail4@mail.local>

$address = "mail1,local<mail1@mail.local>, "mail2@,mail.local"<mail2@mail.local>";

mail1,local<mail1@mail.local>
"mail2@
mail.local" <mail2@mail.local>

mail1,local<mail1@mail.local>
"mail2@mail.local" <mail2@mail.local>