You are trying to receive these emails ?  or send them ?

If receiving can you go to your ISP if they have web mail and delete them there ? That will prevent them from trying to load every time you open Outlook Express. 

If you are sending these and they are not going through you can go to your Outbox and delete them there.

In either case you need to get a program that resizes images. Makes them smaller and nicer to send and receive. Prompt whoever is sending them to you to learn how to shrink them also. 

When I was on dial up had a friend that got a new camera tried to send me about ten 250mb pics in an email. Had me tied up for days and would constantly time out I let it run all night but still no go.

Finally had to get on my ISP at the time and use their web mail to delete the pictures to free up my Outlook Express again.