snail dial-up dealing with Large emails

snail dial-up dealing with Large emails; HELP- I get very large emails that I cannot see-
[before I download] HOW can I see what the email is so I can
Delete or sit and read while it is downloading.

[ps]-new Macintosh user with a Mac Mini-on my Windows computer
I installed a mail-washer to see Email details BEFORE downloading.

any help appreciated, thanks