As someone who has written email and IM compliance software used by 22 of the top 25 banks I can tell you that there is a requirement for data retention of any electronic communication for the vast majority of financial institutions. If you're required by law to archive your communications you need to either comply or get an exemption from your regulator (highly unlikely).

This mitigation strategy only works if the law doesn't require you to retain the data. I've worked at communication companies that only retained email for 7 days, but they weren't obligated to retain their emails by law.