Note that this will match any text between angle brackets. It will also malfunction when presented with multiple <s, which could be a problem if people are discussing math. (e.g., "5<3 according to Bob <bob@somewhere.com>" will give you "3 according to Bob <bob@somewhere.com", not just the actual email address.)

Also note that leading and trailing .* on a regex is just meaningless noise, as the regex will match anywhere in the string by default.

If I were to do this with just a plain regex, I'd go with

$__emailAddressIs =~ /<([^<@>]+@[^<@>]+)>/;
$_sendTo = $1;
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or, a little shorter (but less clear to the uninitiated),

($_sendTo) = $__emailAddressIs =~ /<([^<@>]+@[^<@>]+)>/;
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This will only match a sequence of <, followed by @, followed by >, with each symbol separated from the next by one or more characters other than those three symbols. It's still not perfect (using regexes to determine the validity of an email address is a fool's game), but should be close enough for most purposes.