Correct spelling but wrong word. Spell checkers won't catch usage errors. Put your main message up front. Give adequate information. Summarize the relevant information in the e-mail message.
Long attachments clog the e-mail system and take a long time to download.
Not a BTW to a computer user who missed this point and lost crucial data. Make this a separate e-mail message, or clue in the reader in the subject line or first paragraph. Help the reader digest the message by chunking the information into eyebytes.