If you only use their web-based portal, I'd probably agree. However, I manage several different (work+personal) email addresses via Outlook (the program), including ones from AT&T/Yahoo that I've had for 20+ years.
No issues at all going that route, and they also give you several "alias" accounts as mentioned previously. YMMV...

From another thread:

"I have 5 gmail email addresses.
One is for all the financial and health care institutions I deal with. Nothing but financial and health care emails in and out. No spam.
One for friends and family. ONLY friends and family in and out. No spam.
One address for stuff that's free if you give your email address. Holy crap the amount of spam I get.
One is for on-line merchandise orders. A fair amount of spam, but not un-managable.
The other one hardly gets used, I haven't really assigned a specific use for it yet.

I'm doing this a lot lately. And it has cutdown on the unwanted commercial e-mail. You can never get rid of the Political stuff...

There's also a trick in gmail where it ignores anything after a "+" sign in the email.
So, your email might be "myemail@gmail.com", but you can also get mail at "myemail+spam@gmail.com" and "myemail+advertisement@gmail.com". It'll all come to your Gmail account, and you can use filters to send it to different folders. You can either keep it separate or destroy it, and you can see who Overstock sold your "myemail+onlyforoverstock@gmail.com" email to...