Separate email addresses with ; NOT ,
Keep in mind that simple inconsistencies in the name normalization of email addresses can cause errors in email threading. For example email addresses in the recipient and cc fields should be separated by semi-colons. If they are separated with commas, Relativity will read adjacent email addresses as a single address.
John <email@example.com>, Tom Wilson
. . . will be read as:
John Tom Wilson <firstname.lastname@example.org>