Well, it seems it's kind of charity works, isn't it? Like, if I run a personal server (node) for electeum I am going to help other people trying to use electrum as a light wallet. For me, I don't need to trust anyone else as well. Then where is the different between running a electrum node and bitcoin core node? I guess nothing much. Both are same. Sorry for such question. It might be looking stupid question for you.
It's a mix between charity and running a node for yourself because you don't trust anybody else... There is a difference between running a full node and running an electrum node ON TOP of a bitcoin node: there's quite a bit of overhead, making the minimum specs for a full node smaller than for a full node + electrum node.
I stopped running an electrum node, but i still run a full node...
I have seen at least 3 different electrum server software, one is literally called "electrum personal server" and its quite light. You don't have to open it to others, you can keep it to yourself only, or your own network if you want.
And i clearly remember one of them not needing a full node, a trimmed node works so the requirement is a small as a normal bitcoin node (core wallet). The electrum overhead is pretty minimal especially when private and it could easily run in a raspi.
"Electrumx" is just one of the three, the other two are "Electrum server" and "electrum personal server" (just checked). This is open source, anyone can implement their own server (including malicious actors) it doesn't mean they literally used electrumx, they would have at least modified one of the existing projects or coded their own. Last time they tried a DDoS (when their spammy servers were ignored by newer wallets) i had my own personal server running and did not notice a thing.
And yes its voluntary work if you set up a public server. As with anything public, make sure your server is secure.
i strongly dislike calling them "servers" because it makes it look like a centralized thing you connect to.
Electrumx is the name you can use to describe bitcoin full nodes that have a more advanced P2P protocol compared to regular full nodes such as bitcoin core. they need a bigger storage space because they have to index their blockchain so that they can reply with transaction history based on addresses.
Actually I think that the last year's Electrum hijacking was made with a couple of malicious ElectrumX servers (telling that Electrum needs update and sending out the link to their malicious Electrum) and DDoS on the legit servers, making the users connect to the hacker's servers.
there is nothing important that a malicious Electrum
node can fake. for example they can't give you a fake block header without having to mine it first! which is not possible since it costs a lot to mine a bitcoin block not to mention that you also check the header with other nodes.
or they can't tell you an unconfirmed transaction is confirmed without breaking merkle root's SHA256 which is again impossible.
Electrum is something optional that makes the electrum light "spv?" wallet work. It is exactly as you say, complete with the centralization part. They ARE servers, and they do centralize things. But again, its optional, a convenience for the community, not unlike LN, except unpaid for the operator.
The Electrum wallet needs an electrum server to work, there is no way around that. It does connect to it and
trust it to have current blockchain data and broadcast your transactions. Truly paranoid people should stick with core, or cherry pick the servers they connect to (yes you can choose).
If blockchain.info sets up a public Electrum server, its literally like you said. This is not p2p but server client. Bitcoin remains p2p of course, the servers are working on top of regular bitcoin nodes which ARE p2p.
