AOL, one of the most successful early Internet service providers, started life in 1983 as a company called Control Video Corporation selling downloadable games for the Atari 2600; this became Quantum Computer Services offering online services for the Commodore 64, then Apple, then PC; in 1989 it became known as AOL.
Presumably there was some point at which it started offering email to other customers of the same company (though this might be fuzzy depending on exactly what counts as email).
Presumably there was some later point at which it started offering email to customers of other companies, i.e. Internet email; this seems likely to be more sharply defined.
When did AOL start offering Internet email?