regular expression to match emails
someone@mydomain.com
something1234@mydomain.com
someething.something@mydomain.com
something-something@mydomain.com
something_something@mydomain.com
something_1234@mydomain.com
something.123@mydomain.com
something-456@mydomain.com

[a-zA-Z0-9]+[._-]{1,1}[a-zA-Z0-9]+@mydomain.com

someone@mydomain.com
someont123@mydomain.com

someone_someone_something@mydomain.com

[a-zA-Z0-9]+[._-]{0}[a-zA-Z0-9]+@mydomain.com

something+455@mydomain.com

[a-zA-Z0-9]+[._-]?[a-zA-Z0-9]+@mydomain.com

^[a-zA-Z0-9]+[._-]?[a-zA-Z0-9]+@mydomain.com$