These are all valid email addresses!
- Abc@def@example.com
- Fred\ Bloggs@example.com
- Joe.\Blow@example.com
- “Abc@def”@example.com
- “Fred Bloggs”@example.com
- customer/department=shipping@example.com
- $A12345@example.com
- !def!xyz%abc@example.com
- _somename@example.com
→ https://haacked.com/archive/2007/08/21/i-knew-how-to-validate-an-email-address-until-i.aspx