Provide the right flags to IDN methods for email addresses conversion

[j-bernard]

PHP Mailer converts the email addresses domain to A-label as it does not implement SMTPUTF8 flag but this conversion is not fully IDNA2008 compliant.
The following flags should be provided to idn_to_ascii convertion: IDNA_DEFAULT | IDNA_USE_STD3_RULES | IDNA_CHECK_BIDI | IDNA_CHECK_CONTEXTJ | IDNA_NONTRANSITIONAL_TO_ASCII when using INTL_IDNA_VARIANT_UTS46 variant.
This line should be updated.
A test case would be to provide an email address with domain fußball.test that should be converted to xn--fuball-cta.test instead of fussball.test.

See Unicode IDNA compatibility processing

[Synchro]

Thanks for the pointers. Any chance you could wrap that up into a PR with tests?

[j-bernard]

Yes, let me come back to you when this is ready.