# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/^(([^<>()\[\]\.,;:\s@\"]+(\.[^<>()\[\]\.,;:\s@\"]+)*)|(\".+\"))@(([^<>()[\]\.,;:\s@\"]+\.)+[^<>()[\]\.,;:\s@\"]{2,})/QuestionText = "$1",/gim;t' <<< "prettyandsimple@example.com
very.common@example.com
disposable.style.email.with+symbol@example.com
other.email-with-dash@example.com
x@example.com (one-letter local part)
\"much.more unusual\"@example.com
\"very.unusual.@.unusual.com\"@example.com
\"very.(),:;<>[]\\".VERY.\\"very@\\ \\"very\\".unusual\"@strange.example.com
example-indeed@strange-example.com
admin@mailserver1 (local domain name with no TLD)
#!$%&'*+-/=?^_`{}|~@example.org
\"()<>[]:,;@\\\\"!#$%&'*+-/=?^_`{}| ~.a\"@example.org
\" \"@example.org (space between the quotes)
example@localhost (sent from localhost)
example@s.solutions (see the List of Internet top-level domains)
user@com
user@localserver
user@[IPv6:2001:db8::1]
©other.email-with-dash@example.com
?prettyandsimple@example.com
Invalid email addresses[edit]
Abc.example.com (no @ character)
A@b@c@example.com (only one @ is allowed outside quotation marks)
a\"b(c)d,e:f;g<h>i[j\k]l@example.com (none of the special characters in this local part are allowed outside quotation marks)
just\"not\"right@example.com (quoted strings must be dot separated or the only element making up the local part)
this is\"not\allowed@example.com (spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a backslash)
this\ still\\"not\\allowed@example.com (even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)
john..doe@example.com (double dot before @)
with caveat: Gmail lets this through, Email address#Local-part the dots altogether
john.doe@example..com (double dot after @)"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html