How to Delete HL7 Old Header Data

You can definitely delete from the following HL7 tables as it's really just historical data on messages you've received and sent:

hl7_received_msg_header

hl7_received_msg_data

hl7_sent_msg_data

You can truncate these tables or do regular delete queries.

In order to prevent these from piling up again, it may be helpful to set up a job to automate archiving/deleting the data.