Making up fake email addresses that use real domain names is a bad idea and in my experience also extremely common. To help people avoid that situation, here is a list of all the domain names that I know of that are reserved explicitly for purposes like testing and documentation.
Reserved by RFC2606/RFC6761.
".test" is recommended for use in testing of current or new DNS related code.
Reserved by RFC2606/RFC6761.
".example" is recommended for use in documentation or as examples.
Reserved by RFC2606/RFC6761.
".invalid" is intended for use in online construction of domai names that are sure to be invalid and which it is obvious at a glance are invalid.
Reserved by RFC2606/RFC6761.
The ".localhost" TLD has traditionally been statically defined in host DNS implementations as having an A record pointing to the loop back IP address and is reserved for such use. Any other use would conflict with widely deployed code which assumes this use.
Reserved by RFC2606/RFC6761 for use in documentation and examples.
| DOMAIN | DOMAIN (A-LABEL) | LANGUAGE | SCRIPT |
|---|---|---|---|
| إختبار | xn--kgbechtv | Arabic | Arabic |
| آزمایشی | xn--hgbk6aj7f53bba | Persian | Arabic |
| 测试 | xn--0zwm56d | Chinese | Han (Simplified variant) |
| 測試 | xn--g6w251d | Chinese | Han (Traditional variant) |
| испытание | xn--80akhbyknj4f | Russian | Cyrillic |
| परीक्षा | xn--11b5bs3a9aj6g | Hindi | Devanagari (Nagari) |
| δοκιμή | xn--jxalpdlp | Greek, Modern (1453-) | Greek |
| 테스트 | xn--9t4b11yi5a | Korean | Hangul (Hangŭl, Hangeul) |
| טעסט | xn--deba0ad | Yiddish | Hebrew |
| テスト | xn--zckzah | Japanese | Katakana |