75 KB would be around 7000 words in plain text or about 37 and a half pages of typewriting. If you've just rethought your resolve to compose an average size email, take heed:
- many messages contain formatting information in addition to mere text;
- often, the rich text is accompanied by a duplicate plain text version in the same message;
- newsletters and marketing emails are often longer, bigger emails and make up a large proportion of incoming mail;
- attachments, which can be some 10 MB large, can heavily skew the average.
Average Email Size Heavily Depends on The Mail You Get and Save
The average size of email in your account depends heavily on the kind of email you keep. If you submit photos and drafts and exchange Office files frequently, your average can be closer to 500 KB. If you send back and forth many a small message, the average should be around 15 KB.
A typical 80-word plain text message is around 10 KB.
My personal average email size was 30 KB in 2010.
(Updated August 2012)