For some of them I kind of lost access so I would need to write emails to instagram or whatever, for others I would need to remember and to access to each one of them and delete them.
The hardest would be gmail with people having my contacts from like 10 years ago…
Send an email to people you care about with your new email, they reply or not it’s OK you still have their email address anyway, no big deal.
Source : I’ve migrated away from GMail.