I had the problem of attachments getting divided into pieces when sending e-mail. That was my problem ... The solution is surprinsingly whithin the Outlook Express help:
To send large messages
Many e-mail and news servers limit the size of the messages you can receive and send. Usually this limit is one megabyte (1 MB) per message, including all attached files.
With Outlook Express, you can send large messages or files to e-mail and news servers that have size limits, by breaking the messages into smaller ones. When the group of messages is received, the e-mail program combines them into one message.
On the Tools menu, click Accounts.
On either the Mail or News tab, click Properties.
On the Advanced tab, select the Break apart messages larger than x KB check box and then enter the maximum file size the server will allow.
and my problem was solved. I hope that yours too.
I use Outlook as my email client for both my Hotmail and Yahoo MailPlus aacounts. But I'm unable to send emails with attachments on my Yahoo acct, so I have to resort to do that through the website client. I can recieve attachments just fine, but when I attempt to send email with attachments (not large attachments--text files mostly), my "send/recieve" action times out and re-attempts over and over. Any thoughts?