PHPMailer::validateAddress() fails on PHP 7.3 with libpcre2 < 10.32

[yolabingo]

Due to a bug in libpcre2 < 10.32-RC1 ​https://bugs.exim.org/show_bug.cgi?id=2300,
this email regex validation fails in PHP 7.3 with PCRE_VERSION < 10.32.
One consequence of this is being unable to send a password reset link from the login page - the user sees the error
"The email could not be sent. Possible reason: your host may have disabled the mail() function."

A simple test script ​https://gist.github.com/yolabingo/68b4f037661e702742c5abb324a3d992

PHP < 7.3 uses libpcre 8.x
PHP 7.3 uses libpcre2 10.x

[yolabingo]

simple script to test the

[jrf]

Sounds very similar to #33037 ?