Understanding Exchange Log files

When Exchange receives and email, it first writes it to a log file then commited to the database.
However I noticed under the physical maibox database folder, many E0000000x text documents.
Does that mean the emails that are written to E0000000x text documents have not been received by users (receivers) ? or even when they get commited they stay there untill full back of the DB is applied.

any insight on this will be helpful

thanks