By default, Outlook supports Internationalized Domain Names (IDN) for SMTP addresses in Outlook if Windows provides the appropriate support for this feature. You can disable IDN support so that Punycode rather than native characters are used for rendering SMTP addresses.
You might choose to disable IDN support in Outlook if you do not typically expect non-ASCII characters in SMTP addresses.
This setting does not affect the support of IDN in URLs.
| Registry Hive | HKEY_CURRENT_USER |
| Registry Path | software\policies\microsoft\office\15.0\outlook\options\general |
| Value Name | disableidn |
| Value Type | REG_DWORD |
| Enabled Value | 1 |
| Disabled Value | 0 |