Should I use a seperate but related domain to send reports from my new webapp?

In other webapps I've done I've always sent email from the same domain as the app. However for my next project I'm thinking of using a related domain. For example if my webapp domain was widgets.com the report emails would originate from widgets-reports.com

The app sends daily reports and I'm wary of getting blacklisted as a spammer. The emails are opt-in but in the past I've encountered users flagging automatic email they request as spam instead of disabling emails.

If I send from a related domain I should be able move to a new IP if necessary without disrupting the service's primary email. I really can't think of a downside other than user's expectations that mails would originate from the app domain.

Thoughts?

It's nice to use a separate domain, but not because of black-listing, but rather to give you flexibility in how and where the email service is done.

There are SMTP services you can use that will prevent you from being blacklisted; you may want to investigate e.g. smtp.com or MailChimps.

I like to use separate domains for outbound emails -- it's much more flexible.

The one downside to this is that there is some minimal "brand dilution" (because the domain doesn't exactly match), but I think the tradeoff is worth it.

No. Generally, ISPs blacklist IPs -- not domains. So there is a benefit to using a different IP address from the one you use for outgoing corp email. But the deliverability benefit for using a different domain is smaller than the downside (brand confusion as dharmesh said, maintaining 2 domains, etc).