Is it realistic to refer to someone who lives half a continent from you, as a stalker?
If you know their email address, you can certainly block incoming emails from them, or choose not to ever open anything that they might send.
As they are not local to you - you can choose to not contact them.
And, you should have attempted to block their email address, telephone number and blocked text messages, too.
There's probably not a lot more that you can do, other than contacting law enforcement, but I don't know what they can do when the person lives hundreds of miles from you, in another country.
Don't try to contact that person through any method, even to complain. Don't respond to emails, texts, etc. Not sure how effective it would be to actively refuse any items that you might receive. The idea is to avoid giving this person any additional opportunity to annoy you.
The advice usually given is to write a short, polite - but very clearly stated- and quite explicitly written note, - that is, one email, or letter, requesting that the person cease all contact with you, and not attempt to contact you through third parties. This is so they cannot delude themselves into thinking that you still desire contact and are in no doubt that you do not wish to hear from them.
Stop worrying about an IP address. I'm not sure about Europe but in the US a surprising amount of personal information is public record. And what isn't is often available for a fee. Think background checks and PIs.
Since the stalker isn't exactly close, I agree with the others who said break all contact. Chances are they'll get bored and turn their attention elsewhere. If it persists, definitely seek LE help.
From what I can recall, this is not the first thread the OP has attempted to start on the subject, but it is a serious subject, and irrespective of where the stalker is, it can be rather unnerving to be on the receiving end of such unwelcome attention.
Unfortunately, stalkers tend to be obsessional, and extraordinarily persistent. Aside from entitlement issues, they can be extremely creative. Equally unfortunately, boredom does not usually happen to stalkers , - not when they are thinking about how to resume contact with the object of their pursuit - because their resentment (that someone else took the autonomous decision to end the relationship - whether it was a relationship of colleagues, friends, or something more intimate) fuels their obsessional fury and resentment. In their minds, only they have permission to set the terms on which the relationship starts and ends.
To the OP, block everything, warn common acquaintances that they might be contacted, set up new email addresses, get a new phone number. To be honest, I doubt that IP is relevant.