"An email is your copy, and the sender can’t revise it later."
Sort of. They can't change plain text, but modern emails often include vast swaths of remote content. When you open the message, it retrieves the relevant assets directly from whoever sent the email. That remote content is not permanently stored. It's cached for a bit and will not be re-used if the email is opened months or years later.
If those assets disappear or are changed, there's very little any email provider can do about that.
Sort of. They can't change plain text, but modern emails often include vast swaths of remote content. When you open the message, it retrieves the relevant assets directly from whoever sent the email. That remote content is not permanently stored. It's cached for a bit and will not be re-used if the email is opened months or years later.
If those assets disappear or are changed, there's very little any email provider can do about that.