Email Column Constraint to Contain '@' character
Try this:
CREATE TABLE myTable ( email VARCHAR2(254) );
ALTER TABLE myTable ADD CONSTRAINT chk_email_format CHECK ( REGEXP_LIKE(EMAIL, '.{1,64}@.{1,255}'));


INSERT INTO myTable (email) VALUES ('abc abc.com')
Error report -
SQL Error: ORA-02290: check constraint (FLASHCARD.CHK_EMAIL_FORMAT) violated

254 total characters is from Errata ID: 1690 with 64 before the @ and up to 255 after it.
This simple regexp, email address must have a @, will alert you to attempts to insert wildly wrong data (perhaps helping catch a bug or two).  However, building a complete RFC 5322 validator is a difficult task.  For details take a look here:
https://stackoverflow.com/questions/201323/using-a-regular-expression-to-validate-an-email-address