SigParser has strict rules in place to not allow two contacts to have the same email address in our processing systems.
The most likely cause for seeing multiple email addresses are because there are multiple slightly different spellings of either the name part or the domain part.
Different spellings happen when:
The contact's domain changed at some point
Someone mis-typed the email address and SigParser ingested that email/meeting with the bad email address
Be aware that it is common for the same person to have multiple email address aliases that they receive email to. So the email address might not be wrong, it is just one of their aliases.