When autocompleting an email address, you can start your search with an @ to filter by the hostname first.

For instance, let's assume we want to email a contact named Jack Allen at Twinton University. We don't remember if his email address starts with: jallen@, jack.allen@, jackallen@, j.allen@, etc.

We can just autocomplete starting at @twin:

There he is, right at the top.

You can also autocomplete with the first letter of the mailbox at a specific host, like j*@twin: