Even on a shared account, you can install your own eMail, but squirrelmail, hoarde, and roundcube are all included with cPanel and work with any add-on domains. If you're not needing cPanel hosting, I don't see why you would spend the extra money. if you run into performance issues, WHB will work with you to migrate your account with minimal downtime (I'm sure). I've personally never had any performance issues with my shared hosting from WHB in recent history. you can still have ftp accounts for each domain, eMail addresses, databases, install software with fantastico, etc. http://domain.com/webmail will work for any add-on domain, so you don't even need to give your clients your website as a base-point for getting their webmail. I also suspect that any of your clients are going to actually care what a nameserver is, becaues they sound like my clients. I could tell them the website came from a bunch of people in china that copy-pasted together each page as it was requested, and that the servers themselves ran on the power of bike-pedaling chimpanzees and they'd say "oh, that's nice dear." (Don't call me 'Dear'!!)
Oh, and Google will find your add-on domains just fine, just check out my SEO tips in the "Your Website" part of this forum.
@Alan B: Especially with the economy as it is around here, sometimes lower cost is better than slightly higher efficiency. I do not think a reseller account is really what is needed here.
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