# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(^|;)ab@xyz\.com;/$1/gm;t' <<< "ab@xyz.com;cab@xyz.com;c-ab@xyz.com;c.ab@xyz.com;c_ab@xyz.com;"
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