You have to create a provisioning XML (PROVXML) file to do this -- the email account settings arent in the registry or a file you can back up, but in a system DB on the device. Here's an example of what a PROVXML looks like to create one POP3 email account (replacing the double brackets and what's between them with your own info):
<wap-provisioningdoc>
<characteristic type="EMAIL2">
<characteristic type="{0d06040e-0e09-020f-0b0f-09080e06010b}">
<parm name="CONNECTIONID" value="{436EF144-B4FB-4863-A041-8F905A62C572}" />
<parm name="SERVICENAME" value="[[EMAIL ACCOUNT NAME]]" />
<parm name="SERVICETYPE" value="POP3" />
<parm name="INSERVER" value="[[INCOMING SERVER]]" />
<parm name="OUTSERVER" value="[[OUTGOING SERVER]]" />
<parm name="NAME" value="[[DISPLAY NAME]]" />
<parm name="AUTHNAME" value="[[EMAIL USERNAME]]" />
<parm name="AUTHSECRET" value="[[PASSWORD]]" />
<parm name="DOMAIN" value="" />
<parm name="REPLYADDR" value="[[REPLY-TO ADDRESS]]" />
<parm name="FORMAT" value="2" />
<parm name="LINGER" value="60" />
<parm name="RETRIEVE" value="2048" />
<parm name="KEEPMAX" value="" />
<parm name="DWNDAY" value="-1" />
<characteristic type="TAGPROPS">
<parm name="8128000B" value="1"/>
<parm name="812C000B" value="1"/>
</characteristic>
<parm name="AUTHREQUIRED" value="1" />
<parm name="SMTPALTENABLED" value="0" />
<parm name="SMTPALTAUTHNAME" value="" />
<parm name="SMTPALTPASSWORD" value="" />
</characteristic>
</characteristic>
</wap-provisioningdoc>
Obviously that doesn't look like a lot of fun to code, and it's not. There are some cool tools out there, particularly the Makisu module of SASHIMI that will let you fill out some form questions with your info and then programmatically build the PROVXML for you, so you might want to check that out. I will say that once you move to SASHIMI or UC and get your PROVXMLs built, you'll never go back to any other method of restoring settings. Good luck!