^start of line
Negative Lookahead(?!gmail) gmailthe literal text gmail (case sensitive) .*any Unicode character (except for line terminators), repeated any number of times
mailthe literal text mail (case sensitive) .*?any Unicode character (except for line terminators), repeated any number of times
\s+a Unicode whitespace character, repeated at least once
.*any Unicode character (except for line terminators), repeated any number of times
\s+a Unicode whitespace character, repeated at least once
Athe literal A (6510 / 1018 / 4116) (case sensitive)
\s+a Unicode whitespace character, repeated at least once
.*any Unicode character (except for line terminators), repeated any number of times
$end of line
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
g modifier: global. Finds all matches instead of stopping after the first