If you have a LinkedIn account then make sure you have registered all your email addresses. When someone uploads their contact list, LinkedIn matches their contacts against registered email accounts. If a past colleague or friend has an old or a personal address and you’re only using the new one, the little ‘already LinkedIn’ icon won’t appear and you may miss a chance of reconnecting.
As they say, “Extra email addresses are useful if you expect to be invited at more than one address.”
Go to your profile and select add/edit email. Simple as that.