^start of line
Date:the literal text Date: (case sensitive) \ the literal (3210 / 408 / 2016)
.+?any Unicode character, repeated at least once
$end of line
.+?any Unicode character, repeated at least once
^start of line
From:the literal text From: (case sensitive) \ the literal (3210 / 408 / 2016)
Group sender(?P<sender>.+?$) .+?any Unicode character, repeated at least once
$end of line
.+?any Unicode character, repeated at least once
^start of line
To:the literal text To: (case sensitive) \ the literal (3210 / 408 / 2016)
.+?any Unicode character, repeated at least once
$end of line
.+?any Unicode character, repeated at least once
^start of line
cc:the literal text cc: (case sensitive) \ the literal (3210 / 408 / 2016)
.+?any Unicode character, repeated at least once
$end of line
.+?any Unicode character, repeated at least once
^start of line
Subject:the literal text Subject: (case sensitive) \ the literal (3210 / 408 / 2016)
Group subject(?P<subject>.+?$) .+?any Unicode character, repeated at least once
$end of line
x modifier: extended. Ignores unescaped whitespace and comments outside character classes
s modifier: single line. Allows a dot to match line terminators
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string