I'm able to filter out lines which are complete duplicates of existing ones.

What I can't do is eliminate lines in which just one cell is duplicated.

For example, suppose I have two columns: email addresses and activities.
Someone has an email address alongside tennis and the same email address
alongside golf, but it's the duplicate email address that I want to filter
out. How can I get Excel to eliminate the second line?

Thanks in advance to anyone who replies.

Tim