Word embedding for a single word
There's a bit of confusion about your task: first, apparently by &quot;emails&quot; you mean email addresses, not the full content of the emails, right?
What you're doing looks like record linkage. The complexity of comparing every pair of records (here email addresses) can be decreased using the technique called blocking, where roughly similar pairs are grouped together in order to minimize the number of real comparisons (see Wikipedia page).
Now you're talking about using embeddings, and in this case what you'd need is character embeddings. However it's very unlikely that embeddings will help with the efficiency issue, quite the opposite actually.