Are there some systems that disallow spaces?
Any MTA that doesn't allow sending mail with addresses that contain spaces is not RFC compliant. But every site is free to decide what its policy is for creating email addresses. A site could decide to only allow vowels, or forbid letters or spaces in email addresses.

Abigail

In reply to Re: Simple e-mail validation by Abigail-II
in thread Simple e-mail validation by Anonymous Monk

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