Hi,
this looks like a shoddy attempt at validating an email address... if you're interested in validating email addresses read through the node validate an email address which directs you to several CPAN modules that do this.

If you just want a simple explanation of .+@.+\..+ it says:

• any character (except a newline) (one or more)
• followed by @ (although it should be \@ a plain @ would generate warnings/errors)
• followed by any character (not a newline) (one or more)
• followed by a literal '.'
• followed by any character (not a newline) (one or more)

See perldoc perlre for details.

HTH - Mark