We have a website (Drupal) that provides daily email alerts to about 350 members who have opted in to receive these. In the past we have had small issues with some of our daily alerts being flagged as spam. We are working very hard to make sure that we meet all of the requirements to send legitimate email as our emails are here to help our users. One of those is to use a dedicated email provider such as Mandrill.But one question I have is that my boss thinks that by changing the domain that the email comes from (alert@example.com --> alert@somethingdifferent.com) that it will dodge the spam filters in case someone accidentally marked as spam. I see this as unprofessional.Do major ISP's (like google) look at the IP address of incoming email or the domain, or both?Another question I have is: Is it dangerous at all to have our alert emails come from the same domain as our website? If we have a website www.example.com, with all of our employees having email addresses of employee@example.com, and then have our alerts go out as alerts@example.com - what would happen if the domain were to be blocked? Wouldn't that harm employee emails to our potential members?I would think that it would be more professional to have emails come from our site name, but I just don't want our entire domain to be negatively affected if our alerts gets us in some spam trouble. 
Same or different domain for system emails and company emails?
email;spam;isp
Do major ISP's (like Google) look at the IP address of incoming email  or the domain, or both?Typically they look at the IP address of the mail server using DNSBL databases. These are based on DNS, which resolves IP addresses to domain names. Often spam can be spoofed from a fake email address and domain, and domains do change hands often, so blocking by domain instead of IP would be less accurate. That's not to say that filters and spam reports wouldn't also result in blocked domains by either client applications or incoming mail servers though.Is it dangerous at all to have our alert emails come from the same  domain as our website?Alerts and newsletters often are sent by third-party mail list services, which are specifically setup to address delivery and spam issues. It sounds like you should have your alerts being sent through those, which isn't unprofessional since many sites use them to manage their mailing lists and announcements. 